Optimized thick heteroepitaxial growth of semiconductors with in-situ substrate pretreatment

ABSTRACT

A method of performing HVPE heteroepitaxy comprises exposing a substrate to a carrier gas, a first precursor gas, a Group II/III element, and ternary-forming gasses (V/VI group precursor), to form a heteroepitaxial growth of a binary, ternary, and/or quaternary compound on the substrate; wherein the carrier gas is Hz, wherein the first precursor gas is HCl, the Group II/III element comprises at least one of Zn, Cd, Hg, Al, Ga, and In; and wherein the ternary-forming gasses comprise at least two or more of AsH3 (arsine), PH3 (phosphine), H2Se (hydrogen selenide), HzTe (hydrogen telluride), SbH3 (hydrogen antimonide, or antimony tri-hydride, or stibine), H2S (hydrogen sulfide), NH3 (ammonia), and HF (hydrogen fluoride); flowing the carrier gas over the Group II/III element; exposing the substrate to the ternary-forming gasses in a predetermined ratio of first ternary-forming gas to second ternary-forming gas (1tf:2tf ratio); and changing the 1tf:2tf ratio over time.

PRIORITY

Pursuant to 37 C.F.R. § 1.78(a)(4), this application claims the benefitof and priority to prior filed Provisional Application Ser. No.62/681,155, filed 6 Jun. 2018 and co-pending Non-Provisional applicationSer. No. 16/201,446, filed 27 Nov. 2018, which is expressly incorporatedherein by reference.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

FIELD OF THE INVENTION

The present invention relates generally to heteroepitaxial growth ofsemiconductor materials and, more particularly, to a process for thickheteroepitaxial growth, e.g. hundreds of microns thick layer growth, ofsemiconductor materials based on in-situ pre-growth treatment of thesubstrate.

BACKGROUND OF THE INVENTION

Heteroepitaxy, i.e. the growth of one material on a substrate fromanother material, has a remarkable impact on optics and electronics.Heteroepitaxy is the first choice and sometimes the only availableoption when there is lack of a native substrate. Examples of this aregallium nitride (GaN) and aluminum nitride (AlN) for which nativesubstrates are not available. Accordingly, GaN and AlN continue to begrown mostly on sapphire (Al₂O₃) or on silicon carbide (SiC) substrates.There are a number of other cases, however, where even if nativesubstrates are readily available, heteroepitaxy might still bepreferable. Considerations for such cases are: 1) When the quality ofthe available native substrate is significantly lower, or their pricesignificantly higher, in comparison to the quality and price of readilyavailable non-native alternatives. An example of that is GaP/GaAsheteroepitaxy. Due to the lower etch pit density (EPD) of commercialGaAs (1500-5,000 EP/cm²), compared to the EPD of the commercial GaP(80,000-100,000 EP/cm²), the growth of GaP/GaAs by the Hydride VaporPhase Epitaxy (HYPE) technique usually results in higher surface andcrystalline quality of the heteroepitaxially-grown GaP compared to thehomoepitaxially-grown GaP. In addition, the price of GaP wafers is muchhigher than the price of GaAs wafer, which would increase the cost ofany intended final product; 2) When the related growth technique for thepreparation of a particular substrate material is readily available butthe growth technique still may be incapable of producing large enough(i.e. device size) substrates with the desired surface and crystallinequality. For example, the Physical Vapor Transport (PVT) technique issuitable for the growth of several different materials, e.g. SiC, ZnSe,ZnTe, ZnS, or GaSe boules. However, with the exception of SiC, thematerials comparable to the boule size substrates, which are availableon the market, are mostly polycrystalline; the offered crystallinesamples prepared from such PVT-grown materials are, typically, about 5×5or 10×10 mm. At the same time, even these relatively small “crystalline”samples still consist of at least 3-4 domains with differentcrystallographic orientations, i.e. technically they are not exactlycrystalline. This means that in all these cases (ZnSe, ZnTe, ZnS, GaSe,etc.) the substrate is neither large enough, nor is their quality goodenough for device fabrication; and 3) when, a combination of two or moredifferent materials in a heterostructure sometimes have someundisputable, otherwise unachievable, advantage. One convincing exampleof such a case is the combination of a traditional, universal, andcommon semiconductor material, such as Si (or Ge), with some traditionallinear or nonlinear optical material such as GaAs, GaP, GaSe, ZnSe, ZnS,etc. Si is widely distributed in nature. It is the cheapest and the mostcommon substrate that has the highest material quality among the rest ofthe substrate materials. This may be attributed to the maturity of theavailable industrial growth techniques for its growth, e.g. CZ(Czochralski) growth and EFG (edge-defined film-fed growth). Thesetechniques allow the growth of Si-boules up to 450 mm diameter or oflarge area Si-plates. Si is a unique material with high thermalresistivity, and electrical conductivity that can be easily tuned fromlow to high. This makes Si an attractive substrate for the heteroepitaxyof many of the already mentioned traditional linear and nonlinearoptical materials. This may open the doors to various electronic,optical, or optoelectronic applications.

In order to optimize the growth of other materials on Si-substrates, thegrowth of a number of other electronic and optoelectronic materials(including GaAs and GaP) have been already attempted on Si-substratesusing different growth techniques. Among these growth techniques arewell-known industrial techniques such as Molecular Beam Epitaxy (MBE)and Metal Organic Chemical Vapor Deposition (MOCVD), as well some otherless typical approaches, e.g. Remote Plasma-Enhanced Chemical VaporDeposition (RPECVD) or Liquid Phase Epitaxy (LPE). The opposite cases ofthe growth of silicon on other suitable materials, including GaAs andGaP, have also been investigated.

The most frequent attempts of growth on silicon substrates wereperformed either directly on the Si-substrate or after the deposition ofan intermediate buffer layer (described immediately below), in order toaccommodate the growing layer to the foreign substrate (Si). A greatdeal of effort has been made in engineering those buffer layers.

The choice of Si as a substrate some inconveniences as well, forexample, its fast oxidation, which requires performing specialprior-growth chemical etching procedures to remove this oxide layer.Keeping the substrate in a hot hydrogen flow prior to growth, when thesample is already within the reactor chamber, is also helpful. ReplacingSi with some alternative substrates may eliminate some problems, such asthe need to remove the oxide layer from the substrate surface. However,of course, each replacement material will bring problems that arespecific for each material. One way or another, in most cases, some kindof pre-growth treatment of the substrate will be necessary, either whenit is outside of the reactor or when it is already within the reactorchamber. Such treatments may be necessary to facilitate the initialnucleation, which is the most important stage of the growth because itdetermines all subsequent growth stages. An example of a pre-growthsubstrate treatment is the pre-growth treatment of a sapphire substrateprior to the growth of GaN on it. This procedure is known as“nitridation” of the surface. For this purpose, prior to growth thesapphire substrate is kept for some time at a certain temperature in anammonia (NH₃) flow with the idea to convert a thin region of the topsapphire (Al₂O₃) surface into aluminum nitride (AlN). The usefulness ofthis treatment step is that the lattice mismatch between GaN and AlN ismuch smaller (2.5%) than the lattice mismatch between GaN and sapphire(33%) and, thus, GaN may grow more successfully on AlN than on sapphire.Note: the in-plane lattice mismatch between AlN (0001) and sapphire(0001) is also large, even larger, 35%, than the lattice mismatchbetween GaN and sapphire. Fortunately, when AlN (0001) grows on sapphire(0001), its lattice cell naturally rotates at 30° around its c-axis(which is the [0001] crystallographic direction—the direction of thefastest growth in case of growth of III-Nitrides) with respect to thesapphire lattice cell, which rotation automatically reduces theAlN/sapphire lattice mismatch from 35% to 13.3%, so AlN could growsuccessfully on sapphire. The c-axis is perpendicular to the in-planesurface (0001). The c-axis is visible in FIG. 2A as the [001] axis. Thisis also the most favorable direction for growth. The materials we aregrowing (GaP, GaAs, etc.) are with a cubic zinc blende structure, whilethe III-Nitrides, given here as an example, have a hexagonal wurtzitestructure. To further accommodate the growing GaN layer to the sapphiresubstrate, the nitridation process may be followed by the deposition ofthe so-called low-temperature (LT) AlN or GaN buffer layer—a highlydefective area, which serves to release the strain accumulated duringthe initial stage of heteroepitaxy. The next step in the growth processis the deposition of the intended thick high-temperature (HT) GaN layeron the sapphire substrate.

Next to the lattice mismatch, the thermal mismatch (this is thedifference in the thermal expansion coefficients of the substrate andthe layer materials) is another factor that, along with the differencein the thermal conductivity, should be taken into account whenattempting heteroepitaxial growth, especially thick heteroepitaxialgrowth, because it may result in layer cracking. Because the thermalmismatch has a more significant effect during thick growths, the HVPEgrowth technique, a traditional technique for thick layer growth, wasneglected for a while. Instead, research has been focused for a numberof years on using thin growth techniques, such as MOCVD or MBE. Otheralternative solutions for achieving thick structures may include thewafer bonding technique or in some cases the PVT growth technique. Allthese techniques, of course, have their own disadvantages. Respectively,growths of some other materials, such as ZnSe, GaAs, GaP, GaSb and theirternaries or quaternaries on each other, mostly by MOCVD and MBE, havealso been reported.

In the particular case of nonlinear optical (NLO) materials, such asGaAs, GaP, or ZnSe, especially when the pursued applications wererelated to the development of frequency conversion devices based onquasi-phase matching (QPM), the growth is performed on so-calledorientation-patterned (OP) templates. The typical pattern on such atemplate consists of parallel-striped areas (domains) with periodicallyalternated crystal polarity deposited in a particular crystallographicdirection on a substrate with a particular crystallographic orientation;the domains must have a certain width that satisfies the QPM conditionsfor obtaining conversion to a particular wavelength. In such cases, itis important to optimize thick HVPE growth to form the patternthroughout the whole layer thickness while maintaining good domainfidelity. At the same time, the layer must be thick enough to gain alarge enough aperture for the pump beam and the related wave mixingprocesses to propagate throughout the medium and thus to “ignite” theexpected frequency conversion (FC). In this particular case thesepatterns play a specific optical role and have nothing to do with thepatterned templates mentioned above, which aim to facilitate the initialstages of growth in cases when the related mismatches are relativelylarge.

In the case of epitaxial growth on OP-templates, the heteroepitaxialapproach is similarly preferred for at least two of the several reasonsmentioned above. These are: 1) lack of native OP-templates, or 2) otheradvantages of combining two different materials in a QPM structure. Suchadvantages may be the better quality and/or the lower market price ofthe non-native substrate wafers, the availability of closely matchingnon-native OP templates, the more mature growth process on thealternative material, etc. Due to the first reason, PVT layer growth ofOP-ZnSe (PVT is more known as a bulk growth technique) has beenperformed on OP-GaAs templates with a great deal of confidence, becauseof the small lattice mismatch (+0.24%) between ZnSe and GaAs. Subsequentattempts were used to grow thick GaP; first, on plain GaAs substratesand, later, of OP-GaP on OP-GaAs templates without much hope for successdue to the larger lattice mismatch between GaAs and GaP (−3.57%).Surprisingly, while the first work yielded relatively poor domainfidelity and, therefore, limited optical results, the results from thesecond attempts were successful not only on plain GaAs substrates butalso on OP-GaAs templates.

Unfortunately, at the beginning the resulting heteroepitaxially grownOP-GaP layers were not thick enough for a practical frequency conversiondemonstration. Thus, OP-GaP/OP-GaAs heteroepitaxy was neglected forseveral more years, and research returned to the traditional way, i.e.homoepitaxy of OP-GaP/OP-GaP. However, the preparation of OP-GaPtemplates for the OP-GaP/OP-GaP homoepitaxy revealed some significantshortcomings. Such shortcomings include the low quality (poorparallelism, high EPD), high price, and limited availability of GaPwafers, the presence of an additional absorption band in the infrared(IR) region between 2 and 4 μm, the absence of an etch-stop material(used to secure the thickness of the inverted layer during the waferbonding OP-templates preparation, etc. Therefore, using such wafers inthe fabrication of OP-templates unavoidably resulted in the same poorOP-GaP template quality and, subsequently, in poor HVPE growths on them.Thus the idea to use the 5-6 times cheaper but with much higher qualityOP-GaAs templates, which had been fabricated routinely for a number ofyears for OP-GaAs/OP-GaAs homoepitaxy, came back to the stage again—thistime in support of the OP-GaP/OP-GaAs heteroepitaxy. Thus, after makingsome suitable changes in the reactor configuration and optimizing thegrowth process based on a deeper understanding the process chemistry andgrowth kinetics, we achieved highly repeatable heteroepitaxial growthsof up to hundreds of microns thick OP-GaP layers with excellent domainfidelity on OP-GaAs templates.

The previous work left much to be desired with regard to heteroepitaxialthick growth opportunities. At this point, development in many areas ofoptics and electronics appeared to be almost to their limits, mostlybecause many of the explored materials themselves have achieved theirfundamental or technological limits. However, much unexplored potentialremains for HVPE heteroepitaxy through further engineering of the bufferlayer or through other less explored approaches, especially in the casesof larger lattice and thermal mismatches between the substrate and thegrowing layer. The areas that will be favored by such advancesinclude: 1) optoelectronics: some proper combinations of electronicsemiconductor materials with linear or nonlinear optical materialsrealized by heteroepitaxy or by other flexible growth techniques (orcombinations of growth techniques) may take over other less efficientapproaches, such as wafer bonding, or some less controllable growthtechniques such as, e.g. PVT. This can result in further miniaturizationof ultrafast, all-optically communicating, cost-effective optoelectronicdevices; 2) solar cell industry: even though Si can be grown easily inmature processes, e.g. CZ and EFG, and is still considered as anindisputable leader among the rest of the “solar cell” materials, thereare many material limitations that restrict the efficiency of theSi-solar cells. In this case, heteroepitaxy of other materials on Si(GaAsP/Si as an example) may lead to new types small-dimension,high-power, broad-band hybrid, dual or multi junction solar cellssuitable for various unachieved, yet, applications; 3) multi-materialheterostructures can also favor development of multi-color detectorsthat could cover a wide range of the spectrum; 4) Heteroepitaxy(including van der Waals heteroepitaxy) of 2D or, in general, lowdimensional (LD) materials using foreign substrates; and 5) in the fieldof development of new laser sources heteroepitaxy may allow growths ofphase matching birefringent materials (including of such that have neverbeen grown practically in large monocrystalline substrates) orquasi-phase matching structures and the design of high power, broadlytunable frequency conversion (FC) devices. Such devices could easilyachieve new frequency ranges resulting in various new applications inareas such as defense (IR countermeasures, enhanced laser radar,long-range IR communications), security (remote sensing and spectroscopyof chemical and biological species), industry (automotive pedestrianprotection systems), science (ultrafast spectroscopy of chemicalreaction dynamics), and medicine (breath analysis, biopsy free cancercell detections).

The mechanisms of crystal growth are complex. On a practical level, itis difficult to determine on an atomic scale what exactly occurs afteronly the first few monolayers of growth, even in the simplest cases ofhomoepitaxy of plain semiconductor materials, e.g. Si and Ge. Obviously,heteroepitaxy is a more complex event. This is the real reason why thesemiconductor industry has adopted only a few techniques for slow, thingrowth, e.g. MOCVD and MBE, and for only a few well-studied materials.This is also the reason why thick growth approaches, e.g. HVPE, are usedin only a limited number of homo- and heteroepitaxial cases. In reality,HVPE has never been accepted as a “full” member of the industrialfamily. An additional reason for that is that HVPE (and the other thickgrowth techniques) have their own growth problems such as parasiticnucleation during the HVPE process that, by competing the growth on thesubstrate, reduces the growth rate with the duration of growth andaggravates the layer quality. Another thing that introduces additionalcomplexity is that the thick HVPE growth, especially thickheteroepitaxial growth, requires making certain steps towardsaccommodating the growing layer to the foreign substrates. These stepsmay include some special pretreatments of the substrate before placingthe substrates within the reactor, or after that but prior the actualgrowth. Such thick growths may require prior to the thick HVPE growth athin MOCVD or MBE buffer layer, or to perform a two-step thick growthprocess as the first step to deposit a low temperature (LT) buffer layerand after that, as a second step, to continue with a thick hightemperature (HT) growth.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing problems and othershortcomings, drawbacks, and challenges of heteroepitaxial growth ofsemiconductor materials. While the invention will be described inconnection with certain embodiments, it will be understood that theinvention is not limited to these embodiments. To the contrary, thisinvention includes all alternatives, modifications, and equivalents asmay be included within the spirit and scope of the present invention.

The inventive one-step thick HVPE growth process is preceded by anin-situ pre-growth treatment of the substrate, disclosed and explainedbelow, and is supported by results that confirm that this approachensures a smooth transition between the growing layer and the foreignsubstrates in many material cases, while avoiding other steps that mayexhibit unfavorable impacts on the quality of the growing layer. Thedisclosed process demonstrates that in many cases heteroepitaxy may bethe better choice, even when homoepitaxy is possible. Based on theresults presented below it is suggested that the common belief thathomoepitaxy is always preferable over heteroepitaxy should bereconsidered.

Due to the complex chemistry and specific growth issues for eachmaterial, HYPE is not a traditional industrial technique such as MOCVDand MBE. However, it is the only known approach (excluding wafer bondingor to a small extend the PVT technique) capable of providing thehundreds of microns thick layers which are needed for the applicationsdiscussed below. However, due the nature of its fast growth and, as aresult, poor control of the initial stage of growth, HVPE may often becombined with either growth on patterned templates, or the priordeposition of a low- or high temperature intermediate buffer layer,which may be with a gradually changing chemical composition, called alsoa graded layer. As a close-to-equilibrium process, HVPE may also becombined with a far-from-equilibrium technique, such as MOCVD or MBE. Incontrast to HVPE, such techniques by providing high supersaturationconditions may be used to deposit on the substrate an initial thin layerfrom the same or even other (better matching) material in many caseswhen HVPE cannot do that.

The differences between the MBE or MOCVD and HVPE result in differencesin the buffer layer characteristics. For example, while the MOCVD or MBEbuffer layers are typically only 30-370 nm thick, the HVPE buffer layersmay have a thickness of 3-5 μm or even more. In addition, since MBE andMOCVD are “less sensitive” to lattice mismatch than HYPE, the thin“accommodating” buffer layer deposited between the substrate and theHVPE layer may be of a material different from the substrate materialbut the same as the subsequent HVPE layer material. If this is notpossible, the buffer layer material should be at least with a closelattice match (best within 1% but at least no more than 2-3%) to theHVPE layer material. What a ‘close’ match may depend on a variety ofparameters: sign of the lattice match (sometime a larger negativelattice mismatch is more favorable than a smaller positive latticemismatch), the thermal mismatch and can it compensate the latticemismatch, etc. For example, if the lattice mismatch is positive (thecase of ZnSe/GaAs) the layer will grow under compressive strain, butsince the thermal expansion coefficient of GaAs is larger than thethermal expansion coefficient of ZnSe, this will demand the oppositearrangement, i.e. the layer to grow under tensile strain. In such a casethe opposite strains may favorably partially compensate each other. Inmost situations, a close lattice mismatch is within 1% but no more than2-3%. For examples, GaN may be grown on Si, SiC, or sapphire on apre-deposited thin MOCVD or MBE layer of GaN or AlN; GaN and AlN do nothave a close lattice match with any of the three substrate materials. Incontrast, the HVPE buffer layer shall have a close lattice match withboth the substrate and the growing HVPE layer; the most successful maybe the case where the HVPE buffer layer is a ternary of the parentingsubstrate and layer material. An example is the growth of GaP on GaAs(or vice versa) with the help of an intermediate GaAs_(x)P_(1-x) bufferlayer. The latter, however, is not mandatory; the intermediate HVPEbuffer layer may be from another material with the same requirement,i.e. to match well (more or less, i.e. within 2-3% mismatch) to bothsubstrate and layer material. We may grow, for example, GaAs on a GaPsubstrate or on a GaP buffer layer deposited in advance by afar-from-equilibrium growth process such as MOCVD or MBE on a Sisubstrate. To avoid using other growth techniques this transition GaPlayer may be deposited at a lower than the growth temperature (LT bufferlayer) as a first step of the HVPE growth process prior starting thehigh temperature growth of GaAs on this LT GaP buffer layer. For clarityit should be mentioned that, although a graded buffer intermediate layermay be pursued in both cases (MOCVD or MBE and HVPE) the meaning of“graded” or layer with “gradually changing chemical composition” may bedifferent. For example, when we grow a buffer layer of GaN, changing thecomposition means gradually to change in the V/III ratio, i.e. to changethe ratio between Ga and N, which makes the layer Ga- or N-rich—this maybe achieved by changing the gas flow ratio between the hydride andhalide precursor flows, e.g. between ammonia (NH₃) and GaCl₃ (formed byoverflowing the molten Ga with a flow of HCl). In such a case gradingthe transition buffer layer may change its properties, e.g. the balancein the carrier concentration, but does not practically contribute verymuch to a better mismatch between the buffer and the growing layer,since this is the same material, GaN. In contrast, if one has theintention to grow GaP/GaAs, or the opposite, GaAs/GaP through the HVPEdeposition of a LT transition GaAs_(x)P_(1-x) ternary buffer layer,under composition change we shall have in mind the change in the ratioof arsine (As) and phosphorus (P), i.e. the ratio in the V-group atomsonly (which may be controlled by the arsine to phosphine (AsH₃/PH₃)ratio, keeping the content of the III-group element (Ga), respectivelythe halide precursor (i. e. GaCl₃, formed by overflowing molten Ga witha flow of HCl) the same. Thus, in the case of GaP/GaAs, we may graduallyincrease the content of phosphorus (by increasing the PH₃ flow at theexpense of the AsH₃ flow) for a better fit to the subsequent growth ofGaP. Respectively, in the opposite case of GaAs/GaP growth we maygradually increase the content of arsenic (by increasing the AsH₃ flowat the expense of the PH₃ flow) for a better fit to the subsequentgrowth of GaAs. Adequate changes in the gas flows should be applied toinsure an increasing amount of Ga at the expense of the Al content ifthe goal is to grow GaN on an AlN substrate through the formation of anAlGaN ternary buffer layer, no matter which growth technique is used,i.e. MOCVD, MBE or HVPE. In addition, when Si is the substrate (as anexample), the bandgap energy of a GaAs_(x)P_(1-x) ternary may be “tuned”by changing the x-composition of the ternary to an optimal value thatfits to the bandgap of Si, or another selected substrate. Theoptimization of the heteroepitaxial growth of GaAs_(x)P_(1-x) on aSi-substrate may be useful for realizing a new type portable and highlyefficient, dual junction solar cells.

In some cases, e.g. when the lattice mismatch (i.e. the relativedifference between the lattices of the substrate and the growinglayer—see eq. 1 below) between the Si-substrate and the growing layer islarge—as large as in the case of GaAs growth on Si (4.2% latticemismatch)—growths were purposely performed on so-called patternedtemplates. Note: Herein, a “substrate” is defined as a plain,ready-for-epitaxial-growth surface, while a “template” is a substratethat has a periodic or aperiodic structure, called a “pattern”,deposited or otherwise formed on its surface. The pattern on thetemplate has at least two roles: 1) to provide conditions for a moreuniform nucleation on the template surface, like e.g. evenly distributednucleation spots; and 2) to contribute to a more efficient release ofthe initial strain built in as a result of the lattice and thermalmismatches between substrate and growing layer. This technique isreported to work well with other materials at even larger latticemismatches than those between GaAs and Si, e.g. in cases such as thegrowth of GaSb on patterned GaAs templates (˜7% lattice mismatch).

Next to its major role (to accommodate the growing layer to thesubstrate by providing a more uniform nucleation and facilitating thestrain relief), the buffer layer may also be used for modifying thematerial quality. (Note: As far as a pattern on the substrate mayprovide conditions for more uniform nucleation, it also may beconsidered a buffer layer). For example, the buffer layer may be used tochange the bandgap of the material, as was already pointed to in one ofthe examples, or to achieve better electrical and/or optical materialproperties. For example, it is known that during heteroepitaxy thelattice mismatch between the two materials is the reason for theappearance of a number of dangling (unsatisfied) bonds, which aretypically associated to free carriers. Thus by controlling the number(amount) of dangling bonds one may control the free carrierconcentration and, from here, to modify the material properties.

At this point, along with the various important roles that the bufferlayer plays during heteroepitaxy, there are also a number of seriousproblems associated with its deposition. This means it should beavoided, when possible. The focus of the present invention is toreplace, when possible, the deposition of the buffer layer with in-situsubstrate pretreatment procedures, and when it is not possible, atleast, to make the deposition of such a buffer layer a natural andinseparable stage of a one-step growth process.

According to one embodiment of the present invention a method ofperforming heteroepitaxy, comprises exposing a substrate comprising oneof GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe, CdSe, InSe, ZnTe, CdTe, GaTe,HgTe, GaSb, InSb, AlSb, CdS, ZnS, GaN, AlN, Si, CaF₂, BaF₂, and LiNbO₃(including PPLN) to a carrier gas, a first precursor gas (whichtypically carries a Group II or Group III element), and a secondprecursor gas (which typically is a hydride or halide), to form aheteroepitaxial growth of one of GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe(or GazSe₃), CdSe, InSe, ZnTe, CdTe, GaTe (or GazTe₃), HgTe, GaSb, GaSe,InSb, AlSb, AlAs, InAs, CdS, ZnS, GaN, AlN and some of their ternariessuch as GaAsP, HgCdTe, etc., on the substrate; wherein the carrier gasis Hz, wherein the first precursor is HCl, the Group II or III elementcomprises at least one of Zn, Cd, Hg, Al, Ga, and In, and wherein thesecond precursor is one of AsH₃ (arsine), PH₃ (phosphine), H₂Se(hydrogen selenide), H₂Te (hydrogen telluride), H₂S (hydrogen sulfide),SbH₃ (hydrogen antimonide, called also “stibine”), HF (hydrogenfluoride) and NH₃ (ammonia) or a mixture of some of them. The processmay be an HVPE (hydride vapor phase epitaxy) process (Note: If growingIII-Nitrides when halides are used as a second precursor this processmay be called halide (instead of hydride) vapor phase epitaxy). Morethan one second precursor may be used in a mixture, in varying ratios ofthe mixed single precursor.

According to a first variation of the invention, the substrate is GaAs(gallium arsenide), the second precursor gas is PH₃ (phosphine), and theheteroepitaxial growth is GaP (gallium phosphide).

According to another variation of the invention, the substrate is GaP(gallium phosphide), the second precursor gas is AsH₃ (arsine), and theheteroepitaxial growth is GaAs (gallium arsenide).

According to another variation of the invention, the substrate is GaAs(gallium arsenide), the second precursor gasses are AsH₃ (arsine) andPH₃ (phosphine), and the heteroepitaxial growth is GaAsP (galliumarsenide phosphide).

According to another variation of the invention, the substrate is GaP(gallium phosphide), the second precursor gasses are AsH₃ (arsine) andPH₃ (phosphine), and the heteroepitaxial growth is GaAsP (galliumarsenide phosphide).

According to a further variation of the invention, the substrate is GaAs(gallium arsenide), the second precursor gas is H₂Se (hydrogenselenide), and the heteroepitaxial growth is ZnSe (zinc selenide).

According to another variation of the invention, the substrate is ZnSe(zinc selenide), the second precursor gas is AsH₃ (arsine), and theheteroepitaxial growth is GaAs (gallium arsenide).

According to another variation of the invention, the substrate is GaSb(gallium antimonide), the second precursor gas is H₂Te (hydrogentelluride), and the heteroepitaxial growth is ZnTe (zinc telluride).

According to a further variation of the invention, the substrate is ZnTe(zinc telluride), the second precursor gas is SbH₃ (antimonytri-hydride, called also stibine), and the heteroepitaxial growth isGaSb (gallium antimonide).

According to a further variation of the invention, the substrate is InAs(indium arsenide), the second precursor gas is H₂Te (hydrogentelluride), and the heteroepitaxial growth is ZnTe (zinc telluride).

According to a further variation of the invention, the substrate is ZnTe(zinc telluride), the second precursor gas is AsH₃ (arsine), and theheteroepitaxial growth is InAs (indium arsenide).

According to a further variation of the invention, the substrate is GaN(gallium nitride), the second precursor gas is H₂Se (hydrogen selenide),and the heteroepitaxial growth is ε-GaSe (hexagonal phase GaSe—galliumselenide).

According to another variation of the invention, the substrate is ε-GaSe(hexagonal gallium selenide), the second precursor gas is NH₃ (ammonia),and the heteroepitaxial growth is GaN (gallium nitride).

According to a further variation of the invention, the substrate is GaP(gallium phosphide), the second precursor gas is H₂Se (hydrogenselenide), and the heteroepitaxial growth is Ga₂Se₃ (cubic phase zincblende Ga₂Se₃—gallium selenide).

According to a further variation of the invention, the substrate isGa₂Se₃ (cubic phase zinc blende Ga₂Se₃—gallium selenide), the secondprecursor gas is PH₃ (phosphine), and the heteroepitaxial growth is GaP(gallium phosphide).

According to a further variation of the invention, the substrate is GaAs(gallium arsenide), the second precursor gas is H₂Se (hydrogenselenide), and the heteroepitaxial growth is Ga₂Se₃ (cubic phase zincblende Ga₂Se₃—gallium selenide).

According to a further variation of the invention, the substrate isGa₂Se₃ (cubic phase zinc blende Ga₂Se₃—gallium selenide), the secondprecursor gas is AsH₃ (arsine), and the heteroepitaxial growth is GaAs(gallium arsenide).

According to another variation of the invention, the substrate is AlN(aluminum nitride), the second precursor gas is H₂Se (hydrogenselenide), and the heteroepitaxial growth is ε-GaSe (hexagonal galliumselenide).

According to a further variation of the invention, the substrate isε-GaSe (hexagonal gallium selenide), the second precursor gas is NH₃(ammonia), and the heteroepitaxial growth is AlN (aluminum nitride).

According to a further variation of the invention, the substrate is GaAs(gallium arsenide), the second precursor gas is AsH₃ (arsine), and theheteroepitaxial growth is AlAs (aluminum arsenide).

According to a further variation of the invention, the substrate is AlAs(aluminum arsenide), the second precursor gas is AsH₃ (arsine), theheteroepitaxial growth is GaAs (gallium arsenide).

According to another variation of the invention, the substrate is GaP(gallium phosphide), the second precursor gas is H₂S (hydrogen sulfide),and the growing layer is ZnS (zinc sulfide)

According to another variation of the invention, the substrate is ZnS(zinc sulfide), the second precursor gas is PH₃ (phosphine), and thegrowing layer is GaP (gallium phosphide)

According to another variation of the invention, the substrate is InP(indium phosphide), the second precursor gas is H₂S (hydrogen sulfide),and the heteroepitaxial growth is CdS (cadmium sulfide)

According to another variation of the invention, the substrate is CdS(cadmium sulfide), the second precursor gas is PH₃ (phosphine), and theheteroepitaxial growth is InP (indium phosphide).

According to another variation of the invention, the substrate is InP(indium phosphide), the second precursor gas is H₂Te (hydrogentelluride), and the heteroepitaxial growth is cubic phase zinc blendegallium telluride Ga₂Te₃.

According to another variation of the invention, the substrate is cubicphase zinc blende gallium telluride Ga₂Te₃, the second precursor gas isPH₃ (phosphine), and the heteroepitaxial growth is InP (indiumphosphide).

According to another variation of the invention, the substrate is GaSb(gallium antimonide), the second precursor gas is AsH₃ (arsine), and theheteroepitaxial growth is InAs (indium arsenide).

According to another variation of the invention, the substrate is InAs(indium arsenide), the second precursor gas is SbH₃ (stibine), and theheteroepitaxial growth is GaSb (gallium antimonide).

According to another variation of the invention, the substrate is InAs(indium arsenide), the second precursor gas is H₂Se (hydrogen selenide),and the heteroepitaxial growth is CdSe (cadmium selenide).

According to another variation of the invention, the substrate is CdSecadmium selenide), the second precursor gas is AsH₃ (arsine), and thegrowing layer is InAs (indium arsenide).

According to another variation of the invention, the substrate is InAs(indium arsenide), the second precursor gas is AsH₃ (arsine), and theheteroepitaxial growth is AlAs (aluminum arsenide). (Note: The oppositecase is not presented due to the lack of AlAs substrates).

According to another variation of the invention, the substrate is InAs(indium arsenide), the second precursor gas is SbH₃ (stibine), and theheteroepitaxial growth is AlSb (aluminum antimonide).

According to another variation of the invention, the substrate is AlSb(aluminum antimonide), the second precursor gas is SbH₃ (stibine), andthe heteroepitaxial growth is InAs (indium arsenide).

According to another variation of the invention, the substrate is AlSb(aluminum antimonide), the second precursor gas is SbH₃ (stibine), andthe heteroepitaxial growth is GaSb (gallium antimonide).

According to another variation of the invention, the substrate is GaSb(gallium antimonide), the second precursor gas is SbH₃ (stibine), andthe heteroepitaxial growth is AlSb (aluminum antimonide).

According to another variation of the invention, the substrate is GaSb(gallium antimonide), the second precursor gas is AsH₃ (arsine), and theheteroepitaxial growth is AlAs (aluminum arsenide).

According to another variation of the invention, the substrate is AlAs(aluminum arsenide), the second precursor gas is SbH₃ (stibine), and theheteroepitaxial growth is GaSb (gallium antimonide).

According to another variation of the invention, the substrate is InSb(indium antimonide), the second precursor gas is H₂Te (hydrogentelluride), and the heteroepitaxial growth is CdTe (cadmium telluride).

According to another variation of the invention, the substrate is CdTe(cadmium telluride), the second precursor gas is SbH₃ (stibine), and theheteroepitaxial growth is InSb (indium antimonide)

According to another variation of the invention, the substrate is InSb(indium antimonide), the second precursor gas is H₂Te (hydrogentelluride), and the heteroepitaxial growth is HgTe (mercury telluride).

According to another variation of the invention, the substrate is HgTe(mercury telluride), the second precursor gas is SbH₃ (stibine), and theheteroepitaxial growth is InSb (indium antimonide).

According to another variation of the invention, the substrate is CdTe(cadmium telluride), the second precursor gas is H₂Te (hydrogentelluride), and the heteroepitaxial growth is HgTe (mercury telluride).

According to another variation of the invention, the substrate is HgTe(mercury telluride), the second precursor gas is H₂Te (hydrogentelluride), and the heteroepitaxial growth is CdTe (cadmium telluride).

According to another variation of the invention, the substrate is InSb(indium antimonide), CdTe (cadmium telluride) or HgTe (mercurytelluride). The second precursor gas is H₂Te (hydrogen telluride), andthe heteroepitaxial growth is HgCdTe (mercury cadmium telluride).

According to another variation of the invention, the substrate is HgCdTe(mercury cadmium telluride), the second precursor gas is H₂Te (hydrogentelluride), and the heteroepitaxial growth is CdTe (cadmium telluride)or HgTe (mercury telluride), or if the second precursor gas is SbH₃(hydrogen antimonide) the heteroepitaxial growth is InSb (indiumantimonide),

According to another variation of the invention, the substrate is from amaterial that is suitable for growth of InSe (indium selenide), thesecond precursor gas is H₂Se (hydrogen selenide), and theheteroepitaxial growth performed through van der Waals heteroepitaxy isInSe (indium selenide). (Note: The opposite case is not presented due tothe lack of InSe substrates).

According to another variation of the invention, the substrate is CaF₂(calcium fluoride), the second precursor gas is PH₃ (phosphine), and theheteroepitaxial growth is GaP (gallium phosphide). (Note: The oppositecase is not presented as less interesting from practical point of view).

According to another variation of the invention, the substrate is CaF₂(calcium fluoride), the second precursor gas is AsH₃ (arsenide), and theheteroepitaxial growth is GaAs (gallium arsenide). (Note: The oppositecase is not presented as less interesting from practical point of view).

According to another variation of the invention, the substrate is BaF₂(barium fluoride), the second precursor gas is SbH₃ (hydrogenantimonide), and the heteroepitaxial growth is AlSb (aluminumantimonide). (Note: The opposite case is not presented as lessinteresting from practical point of view).

According to another variation of the invention, the substrate is BaF₂(barium fluoride), the second precursor gas is SbH₃ (hydrogenantimonide), and the heteroepitaxial growth is GaSb (galliumantimonide). (Note: The opposite case is not presented as lessinteresting from practical point of view).

According to another variation of the invention, the substrate is LiNbO₃(lithium niobate) or periodically poled lithium niobate (PPLN), thesecond precursor gas is PH₃ (phosphine), and the heteroepitaxial growthis GaP (gallium phosphide) or OP-GaP. (Note: The opposite case is notpresented as less interesting from practical point of view).

According to another variation of the invention, the substrate is LiNbO₃(lithium niobate) or periodically poled lithium niobate (PPLN), thesecond precursor gas is AsH₃ (arsine), and the heteroepitaxial growth isGaAs (gallium arsenide) or OP-GaAs. (Note: The opposite case is notpresented as less interesting from practical point of view).

According to a second embodiment of the invention, a method ofperforming heteroepitaxy, comprises exposing a substrate to a carriergas, a first precursor gas, a Group II/III element, and ternary-forminggasses (V/VI group precursor), to form a heteroepitaxial growth of oneof GaAs, AlAs, InAs, GaP, InP, ZnSe, GaSe (or Ga₂Se₃), CdSe, InSe, ZnTe,CdTe, GaTe (or Ga₂Te₃), HgTe, GaSb, GaSe, InSb, AlSb, AlAs, InAs, CdS,ZnS, GaN, AlN and some of their ternaries such as GaAsP, HgCdTe, etc. onthe substrate; wherein the substrate comprises one of GaAs, AlAs, InAs,GaP, InP, ZnSe, GaSe (or Ga₂Se₃), CdSe, InSe, ZnTe, CdTe, GaTe (orGa₂Te₃), HgTe, GaSb, InSb, AlSb, CdS, ZnS, GaN, AlN, Si, CaF₂, BaF₂, andLiNbO₃ (including PPLN); wherein the carrier gas is Hz, wherein thefirst precursor gas is HCl, the Group II/III element comprises at leastone of Zn, Cd, Hg, Al, Ga, and In; and wherein the ternary-forminggasses comprise at least two or more of AsH₃ (arsine), PH₃ (phosphine),H₂Se (hydrogen selenide), H₂Te (hydrogen telluride), SbH₃ (hydrogenantimonide, or antimony tri-hydride, or stibine), H₂S (hydrogensulfide), NH₃ (ammonia), and HF (hydrogen fluoride); flowing the carriergas over the Group II/III element; exposing the substrate to theternary-forming gasses in a predetermined ratio of first ternary-forminggas to second ternary-forming gas (1tf:2tf ratio); and changing the1tf:2tf ratio over time.

According to a first variation of this embodiment, the method furthercomprises flowing the ternary-forming gasses through the furnace at a1tf:2tf ratio of about 1:0; heating the substrate to about 500° C.-900°C.; and gradually changing the 1tf:2tf ratio towards 0:1, or to anyother ratio between 1:0 to 0:1, over a time period of 1 min-10 hours.One of the gas flows may be as much as 20× smaller than the other. Thefinal targeted 1tf:2tf ratio may be anywhere between 1:0 and 0:1, e.g.1:2, 1:4, 1:8, 1:10, 0.5:10, 0.5:20, or any other ratio, depending onthe particular gases and conditions in the reactor.

According to another variation of this embodiment, the Group II/IIIelement is Ga, the substrate is GaAs (gallium arsenide), the firstternary-forming gas is AsH₃, the second ternary-forming gas is PH₃(phosphine), and the heteroepitaxial growth is GaP (gallium phosphide).This corresponds to GaP on GaAs, i.e. GaP/GaAs.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is GaP (gallium phosphide), thefirst ternary-forming gas is PH₃, the second ternary-forming gas is AsH₃(arsine), and the heteroepitaxial growth is GaAs (gallium arsenide).This corresponds to GaAs on GaP.

According to another variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is GaAs (gallium arsenide), thefirst ternary-forming gas is AsH₃ (arsine), the second ternary-forminggas is PH₃ (phosphine), and the heteroepitaxial growth is GaAsP (galliumarsenide phosphide). This corresponds to GaAsP on GaAs.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is GaP (gallium phosphide), thefirst ternary-forming gas is PH₃ (phosphine), the second ternary-forminggas is AsH₃ (arsine), and the heteroepitaxial growth is GaAsP (galliumarsenide phosphide). This corresponds to GaAsP on GaP.

According to another variation of this embodiment, the Group II/IIIelement is Zn, wherein the substrate is GaAs (gallium arsenide), thesecond ternary-forming gas is AsH₃, the second ternary-forming gas isH₂Se (hydrogen selenide), and the heteroepitaxial growth is ZnSe (zincselenide). This corresponds to ZnSe on GaAs.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is ZnSe (zinc selenide), the firstternary-forming gas is H₂Se, the second ternary-forming gas comprisesAsH₃ (arsine), and the heteroepitaxial growth is GaAs (galliumarsenide). This corresponds to GaAs on ZnSe.

According to another variation of this embodiment, the Group II/IIIelement is Zn, wherein the substrate is GaSb (gallium antimonide), thefirst ternary-forming gas is SbH₃, the second ternary-forming gas isH₂Te (hydrogen telluride), and the heteroepitaxial growth is ZnTe (zinctelluride). This corresponds to ZnTe on GaSb.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is ZnTe (zinc telluride), the firstternary-forming gas is H₂Te, the second ternary-forming gas is SbH₃(hydrogen antimonide/stibine/antimony tri-hydride), and theheteroepitaxial growth is GaSb (gallium antimonide). This corresponds toGaSb on ZnTe.

According to another variation of this embodiment, the Group II/IIIelement is Zn, wherein the substrate is InAs (indium arsenide), thefirst ternary-forming gas is AsH₃, the second ternary-forming gas isH₂Te (hydrogen telluride), and the heteroepitaxial growth is ZnTe (zinctelluride). This corresponds to ZnTe on InAs.

According to a further variation of this embodiment, the Group II/IIIelement is In, wherein the substrate is ZnTe (zinc telluride), the firstternary-forming gas is H₂Te, the second ternary-forming gas is AsH₃(arsine), and the heteroepitaxial growth is InAs (indium arsenide). Thiscorresponds to InAs on ZnTe.

According to another variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is GaN (gallium nitride), the firstternary-forming gas is NH₃, the second ternary-forming gas is H₂Se(hydrogen selenide), and the heteroepitaxial growth is hexagonal ε-GaSe(gallium selenide). This corresponds to hexagonal GaSe on GaN.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is hexagonal ε-GaSe (galliumselenide), the first ternary-forming gas is H₂Se, the secondternary-forming gas is NH₃ (ammonia), and the heteroepitaxial growth isGaN (gallium nitride). This corresponds to GaN on hexagonal GaSe.

According to another variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is GaP (gallium phosphide), thefirst ternary-forming gas is PH₃, the second ternary-forming gas is H₂Se(hydrogen selenide), and the heteroepitaxial growth is cubic phase zincblende gallium selenide Ga₂Se₃. This corresponds to cubic phase zincblende Ga₂Se₃ on GaP.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is cubic phase zinc blende galliumselenide Ga₂Se₃, the first ternary-forming gas is H₂Se, the secondternary-forming gas is PH₃ (phosphine), and the heteroepitaxial growthis GaP (gallium phosphide). This corresponds to GaP on cubic phase zincblende gallium selenide Ga₂Se₃.

According to another variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is GaAs (gallium arsenide), thefirst ternary-forming gas is AsH₃, the second ternary-forming gas isH₂Se (hydrogen selenide), and the heteroepitaxial growth is cubic phasezinc blende gallium selenide Ga₂Se₃. This corresponds to cubic phasezinc blende gallium selenide Ga₂Se₃ on GaAs.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, wherein the substrate is cubic phase zinc blende galliumselenide Ga₂Se₃, the first ternary-forming gas is H₂Se, the secondternary-forming gas is AsH₃ (arsine), and the heteroepitaxial growth isGaAs (gallium arsenide). This corresponds to GaAs on cubic phase zincblende gallium selenide Ga₂Se₃.

According to another variation of this embodiment, the Group II/IIIelement is Ga, the substrate is AlN (aluminum nitride), the firstternary-forming gas is NH₃, the second ternary-forming gas is H₂Se(hydrogen selenide), and the heteroepitaxial growth is hexagonal ε-GaSe(gallium selenide). This corresponds to hexagonal GaSe on AlN.

According to a further variation of this embodiment, the Group II/IIIelement is Al, the substrate is hexagonal ε-GaSe (gallium selenide), thefirst ternary-forming gas is H₂Se, the second ternary-forming gas is NH₃(ammonia), and the heteroepitaxial growth is AlN (aluminum nitride).This corresponds to AlN on hexagonal GaSe.

According to another variation of this embodiment, the Group II/IIIelement is Al, the substrate is GaAs (gallium arsenide), the firstternary-forming gas is AsH₃, the second ternary-forming gas is AsH₃(arsine), and the heteroepitaxial growth is AlAs (aluminum arsenide).This corresponds to AlAs on GaAs. Since GaAs and AlAs are botharsenides, there is no need of a mixture of ternary gases. The oppositegrowth, GaAs/AlAs, is not presented because of the lack of AlAssubstrates. However, the lattice mismatch between GaAs and AlAs isnegligible (+0.127%). High quality GaAs substrates and OP-GaAs templatesare both readily available. Accordingly, heteroepitaxial growth of highquality AlAs on GaAs and even on OP-GaAs is very possible.

According to a further variation of this embodiment, the Group II/IIIelement is Zn, the substrate is GaP (gallium phosphide), the firstternary-forming gas is PH₃, the second ternary-forming gas is H₂S(hydrogen sulfide), and the heteroepitaxial growth is ZnS (zincsulfide). This corresponds to ZnS on GaP.

According to another variation of this embodiment, the Group II/IIIelement is Ga, the substrate is ZnS (zinc sulfide), the firstternary-forming gas is H₂S, the second ternary-forming gas is PH₃(phosphine), and the heteroepitaxial growth is GaP (gallium phosphide).This corresponds to GaP on ZnS.

According to a further variation of this embodiment, the Group II/IIIelement is Cd, the substrate is InP (indium phosphide), the firstternary-forming gas is PH₃, the second ternary-forming gas is H₂S(hydrogen sulfide), and the heteroepitaxial growth is CdS (cadmiumsulfide). This corresponds to CdS on InP.

According to another variation of this embodiment, the Group II/IIIelement is In, the substrate is CdS (cadmium sulfide), the firstternary-forming gas is H₂S, the second ternary-forming gas is PH₃(phosphine), and the heteroepitaxial growth is InP (indium phosphide).This corresponds to InP on CdS.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, the substrate is InP (indium phosphide), the firstternary-forming gas is PH₃, the second ternary-forming gas is H₂Te(hydrogen telluride), and the heteroepitaxial growth is a cubic phasezinc blende gallium telluride Ga₂Te₃. This corresponds to cubic phasezinc blende gallium telluride Ga₂Te₃ on InP. The opposite growth(InP/Ga₂Te₃) is not presented as being less reasonable.

According to another variation of this embodiment, the Group II/IIIelement is In, the substrate is GaSb (gallium antimonide), the firstternary-forming gas is SbH₃, the second ternary-forming gas is AsH₃(arsine), and the heteroepitaxial growth is InAs (indium arsenide). Thiscorresponds to InAs on GaSb.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, the substrate is InAs (indium arsenide), the firstternary-forming gas is AsH₃, the second ternary-forming gas is SbH₃(hydrogen antimonide), and the heteroepitaxial growth is GaSb (galliumantimonide). This corresponds to GaSb on InAs.

According to another variation of this embodiment, the Group II/IIIelement is Cd, the substrate is InAs (indium arsenide), the firstternary-forming gas is AsH₃, the second ternary-forming gas is H₂Se(hydrogen selenide), and the heteroepitaxial growth is CdSe (cadmiumselenide). This corresponds to CdSe on InAs. The opposite growth(InAs/CdSe) is not presented as being less reasonable.

According to a further variation of this embodiment, the Group II/IIIelement is Al, the substrate is InAs (indium arsenide), the first andthe second ternary-forming gas is the same AsH₃ (arsine), and theheteroepitaxial growth is AlAs (aluminum arsenide). Since both substrate(InAs) and growing layer (AlAs) are arsenides, only AsH₃ is used. Thiscorresponds to AlAs on InAs. The opposite growth (InAs/AlAs) is notpresented as being less reasonable.

According to another variation of this embodiment, the Group II/IIIelement is Al, the substrate is InAs (indium arsenide), the firstternary-forming gas is AsH₃, the second ternary-forming gas is SbH₃(hydrogen antimonide), and the heteroepitaxial growth is AlSb (aluminumantimonide). This corresponds to AlSb on InAs. The opposite growth(InAs/AlSb) is not presented as being less reasonable.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, the substrate is AlSb (aluminum antimonide), the firstternary-forming gas is SbH₃, the second ternary-forming gas is SbH₃(hydrogen antimonide), and the heteroepitaxial growth is GaSb (galliumantimonide). This corresponds to GaSb on AlSb. Since GaSb and AlSb areboth antimonides, there is no need of a gas mixture.

According to another variation of this embodiment, the Group II/IIIelement is Al, the substrate is GaSb (gallium antimonide), the firstternary-forming gas is SbH₃, the second ternary-forming gas is SbH₃(hydrogen antimonide), and the heteroepitaxial growth is AlSb (aluminumantimonide). This corresponds to AlSb on GaSb. Since GaSb and AlSb areboth antimonides, there is no need of a mixture of gases.

According to a further variation of this embodiment, the Group II/IIIelement is Al, the substrate is GaSb (gallium antimonide), the firstternary-forming gas is SbH₃, the second ternary-forming gas is AsH₃(arsine), and the heteroepitaxial growth is AlAs (aluminum arsenide).This corresponds to AlAs on GaSb.

According to another variation of this embodiment, the Group II/IIIelement is Ga, the substrate is AlAs (aluminum arsenide), the firstternary-forming gas is AsH₃, the second ternary-forming gas is SbH₃(hydrogen antimonide), and the heteroepitaxial growth is GaSb (galliumantimonide). This corresponds to GaSb on AlAs.

According to a further variation of this embodiment, the Group II/IIIelement is Cd, the substrate is InSb (indium antimonide), the firstternary-forming gas is SbH₃, the second ternary-forming gas is H₂Te(hydrogen telluride), and the heteroepitaxial growth is CdTe (cadmiumtelluride). This corresponds to CdTe on InSb. The opposite growth(InSb/CdTe) is not presented as being less reasonable.

According to another variation of this embodiment, the Group II/IIIelement is Hg, the substrate is InSb (indium antimonide), the firstternary-forming gas is SbH₃, the second ternary-forming gas is H₂Te(hydrogen telluride), and the heteroepitaxial growth is HgTe (mercurytelluride). This corresponds to HgTe on InSb. The opposite growth(InSb/HgTe) is not presented as being less reasonable.

According to a further variation of this embodiment, the Group II/IIIelement is Hg, the substrate is CdTe (cadmium telluride), the firstternary-forming gas is H₂Te, the second ternary-forming gas is H₂Te, andthe heteroepitaxial growth is HgTe (mercury telluride). This correspondsto HgTe on CdTe. Since CdTe and HgTe are both tellurides, there is noneed of a gas mixture. The opposite growth (CdTe/HgTe) is not presentedas being less reasonable.

According to another variation of this embodiment, the Group II/IIIelement is Hg, the substrate is either InSb (indium antimonide), CdTe(cadmium telluride) or HgTe (mercury telluride). The the first andsecond ternary-forming gases in the cases of growth on CdTe or HgTe isH₂Te (hydrogen telluride), because the two substrates choices (CdTe andHgTe) and the growing layer (HgCdTe) are tellurides. When InSb is usedas a substrate, H₂Te is the first ternary-forming gas, but SbH₃(hydrogen antimonide) may be used as a second ternary-forming gas. Theheteroepitaxial growth in all this cases is HgCdTe (mercury cadmiumtelluride). This corresponds to HgCdTe on one of the substrates, i.e.InSb, CdTe, or HgTe. Note: HCl overflows a first boat with Hg and asecond boat with molten Cd, and only H₂Te is used as a ternary-precursorgas in the cases of HgCdTe growth on CdTe or HgTe substrates. In thecase of HgCdTe growth on an InSb substrate, growth may start in aSbH₃+H₂Te mixture to allow a smoother transition between the substrateand the growing HgCdTe layer. The opposite growths (InSb/HgCdTe,CdTe/HgCdTe and HgTe/HgCdTe) are not presented.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, the substrate is CaF₂ (calcium fluoride), the firstternary-forming gas is HF, the second ternary-forming gas is PH₃(phosphine), and the heteroepitaxial growth is GaP (gallium phosphide).This corresponds to GaP on CaF₂. The opposite growth (CaF₂/GaP) is notpresented because CaF₂ is not transparent in the wavelength range ofinterest.

According to another variation of this embodiment, the Group II/IIIelement is Ga, the substrate is CaF₂ (calcium fluoride), the firstternary-forming gas is HF, the second ternary-forming gas is AsH₃(arsenide), and the heteroepitaxial growth is GaAs (gallium arsenide).This corresponds to GaAs on CaF₂. The opposite growth (CaF₂/GaAs) is notpresented because CaF₂ is not transparent in the wavelength range ofinterest.

According to a further variation of this embodiment, the Group II/IIIelement is Al, the substrate is BaF₂ (barium fluoride), the firstternary-forming gas is HF, the second ternary-forming gas is SbH₃(hydrogen antimonide), and the heteroepitaxial growth is AlSb (aluminumantimonide). This corresponds to AlSb on BaF₂. The opposite growth(BaF₂/AlSb) is not presented because BaF₂ is not transparent in thewavelength range of interest.

According to another variation of this embodiment, the Group II/IIIelement is Ga, the substrate is BaF₂ (barium fluoride), the firstternary-forming gas is HF, the second ternary-forming gas is SbH₃(hydrogen antimonide), and the heteroepitaxial growth is GaSb (galliumantimonide. This corresponds to GaSb on BaF₂. The opposite growth(BaF₂/GaSb) is not presented because BaF₂ is not transparent in thewavelength range of interest.

According to a further variation of this embodiment, the Group II/IIIelement is Ga, the substrate is one of LiNbO₃ (Lithium niobate) orperiodically poled lithium niobate (PPLN), the first ternary-forming gasis PH₃, the second ternary-forming gas is PH₃ (phosphine), and theheteroepitaxial growth is one of GaP (gallium phosphide) or OP-GaP. Thiscorresponds to GaP on LiNbO₃ or OP-GaP on LiNbO₃. The opposite growth(LiNbO₃/GaP) is not shown because LiNbO₃ is transparent only in a partof the wavelength range of interest.

According to another variation of this embodiment, the Group II/IIIelement is Ga, the substrate is one of LiNbO₃ (lithium niobate) orperiodically poled lithium niobate (PPLN), the first ternary-forming gasis AsH₃, the second ternary-forming gas is AsH₃ (arsine), and theheteroepitaxial growth is one of GaAs (gallium arsenide) or OP-GaAs.This corresponds to GaAs on LiNbO₃ or OP-GaAs on LiNbO₃. The oppositegrowth (LiNbO₃/GaAs) is not shown because LiNbO₃ is transparent only ina part of the wavelength range of interest.

Details regarding these and other heteroepitaxial cases can be found inFIG. 13 .

Additional objects, advantages, and novel features of the invention willbe set forth in part in the description, which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentinvention and, together with a general description of the inventiongiven above, and the detailed description of the embodiments givenbelow, serve to explain the principles of the present invention. Thepatent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 illustrates the energy gap as a function of the lattice constantsfor some traditional compound semiconductor materials;

FIG. 2A illustrates that the biaxial strain a can be resolved into auniaxial shear stress τ on the {111} dislocation glide plane;

FIG. 2B presents a TEM image of the strain being relaxed in a plastic(dislocation nucleation) process during GaP/GaAs heteroepitaxy;

FIG. 3A presents an SEM image of a GaAs substrate preheated for 1 h inAsH₃+H₂ atmosphere, according to an embodiment of the invention;

FIG. 3B presents an SEM image of a GaAs substrate preheated in H₂atmosphere only and shows the damages in result of the thermaldecomposition of the GaAs surface.

FIG. 3C presents an SEM image with a higher magnification of a GaAssubstrate preheated for 1 h in PH₃:H₂ atmosphere.

FIG. 3D presents an AFM images of a small area from the SEM image shownon FIG. 3C;

FIG. 4A presents an AFM image at lower magnification than FIGS. 3D, 4Cand 4D of a GaAs substrate preheated for 1 h in PH₃:H₂ atmosphere,according to an embodiment of the invention;

FIG. 4B presents an AFM image at lower magnification of a GaP substratepreheated for 1 h in AsH₃:H₂ atmosphere, according to an embodiment ofthe invention;

FIG. 4C presents an AFM image of a small area of FIG. 4A at a highermagnification of a GaAs substrate preheated for 1 h in PH₃:H₂atmosphere, according to an embodiment of the invention;

FIG. 4D presents an AFM image of a small area of FIG. 4B at a highermagnification of a GaP substrate preheated for 1 h in AsH₃:H₂atmosphere, according to an embodiment of the invention;

FIG. 5 presents the thermal decomposition of AsH₃ and PH₃ as a functionof the temperature in a quartz vessel with (the two curves at left) andwithout (the two curves at right) the presence of a GaAs (with arsineflow) or a GaP (with phosphine flow) substrates within the vessel;

FIG. 6A presents an SEM image of a GaAs substrate preheated in PH₃:H₂atmosphere;

FIGS. 6B-6C present an EDS analysis that showing the presence of onlyGaAs in the pitted (dark) spots (FIG. 6B); in contrast, the partlycovered (white) areas indicate the presence of GaAsP (FIG. 6C);

FIG. 7A presents a SEM cross section image of an area near thesubstrate/layer interface that shows the formation of an intermediatelayer between the GaAs substrate and the growing GaP layer;

FIG. 7B presents an EDS profile analysis that indicates that the formingbuffer layer is a GaAsP ternary with a gradually changing composition;

FIG. 8 presents a Nomarski cross section image of a grown multilayerhetero-structure first of GaAs/GaAs and after that of GaP/GaAs;

FIGS. 9A-9D present SEM top surface images of an OP-GaAs templateshowing the adjacent area around the boundary between two oppositelyoriented domains before preheating (FIG. 9A) and after preheating inPH₃:H₂ atmosphere (FIG. 9B). Respectively, (FIG. 9C) represents the areawithin the green shaped rectangular from FIG. 9B at a largermagnification, while FIG. 9D represents the area within the red shapedrectangular from FIG. 9B. There, due to the increased magnification, onecan see how the longitudinally-shaped pits that appear after theexposure of the GaAs substrate to the non-native precursor (PH₃:H₂) areoriented in two mutually perpendicular directions in the two neighboringdomains with opposite crystallographic orientations; (FIG. 9E) presentsa Nomarski cross section image of a 138 μm thick OP-GaP grownheteroepitaxially on the same OP-GaAs template shown in the previousFIGS. 9A-9D, according to an embodiment of the invention;

FIG. 10A illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of GaP with in-situ pre-growthtreatment of the GaAs substrate or the template, according to anembodiment of the invention;

FIG. 10B illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of GaAs with in-situ pre-growthtreatment of the GaP substrate or the template, according to anembodiment of the invention;

FIG. 10C illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of GaAs_(x)P_(1-x) ternaries within-situ pre-growth treatment of the GaAs or GaP substrate or thetemplate, according to an embodiment of the invention;

FIG. 10D illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of ZnSe with in-situ pre-growthtreatment of the GaAs substrate or the template, according to anembodiment of the invention;

FIG. 10E illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of GaAs with in-situ pre-growthtreatment of the ZnSe substrate or the template, according to anembodiment of the invention;

FIG. 10F illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of a cubic phase zinc blendegallium selenide Ga₂Se₃ with in-situ pre-growth treatment of the GaPsubstrate or the template, according to an embodiment of the invention;

FIG. 10G illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of a cubic phase zinc blendegallium selenide Ga₂Se₃ with in-situ pre-growth treatment of the GaAssubstrate or the template, according to an embodiment of the invention;

FIG. 10H illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of ε-GaSe with in-situ pre-growthtreatment of the GaN substrate or the template, according to anembodiment of the invention;

FIG. 10I illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of ZnTe on GaSb or InAssubstrates with in-situ pre-growth treatment of the GaSb or InAssubstrate or template, according to an embodiment of the invention;

FIG. 10J illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of ZnS and CdS with in-situpre-growth treatment of the GaP or, respectively, the InP substrate orthe related templates, according to an embodiment of the invention;

FIG. 10K illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of GaSb and AlSb on InAssubstrates and AlSb on GaSb substrates with in-situ pre-growth treatmentof the InAs or, respectively, the GaSb substrate or the relatedtemplates, according to an embodiment of the invention;

FIG. 10L illustrates a schematic drawing of an HVPE apparatus foroptimized thick heteroepitaxial growth of AlAs on GaAs with in-situpre-growth treatment of the GaAs substrate or the OP-GaAs template,according to an embodiment of the invention;

FIG. 11 depicts the thickness of the pseudomorphous growth (the criticalthickness h_(c)) expressed as the number of monoatomic layers as afunction of the lattice mismatch ƒ,

FIGS. 12A-12C depict TEM cross sectional images with increasingmagnification showing rough surface interface between the growing GaPlayer and the GaAs substrate;

FIG. 12D depicts that compositional variations and distortions ofdifferent kind, such as creating of voids or roughening of surfaces nearthe interface make difficult to determine the thickness of thepseudomorphous growth h_(c) and the periodicity τ of the MDs.

FIGS. 13A-13B present tables with some of the favorable heteroepitaxialcases from point of view of the lattice mismatches. The most probablechemistry in each individual case is also included in the table.

FIGS. 14A-14F depict SEM images of heteroepitaxial growth of ZnSe onplain GaAs substrates as (FIG. 14A) is a cross sectional image, and(FIG. 14B) is a top surface image. These images are compared to SEMimages of homoepitaxial growth of ZnSe on a ZnSe substrate as (FIG. 14C)is cross section image, and (FIG. 14D) is a top surface image.

FIGS. 15A-15B depicts cross-sectional TEM image of the HVPE grownZnSe/GaAs: as (FIG. 15A) shows bright-field planar image withcorresponding FFT patterns; (FIG. 15B) shows high-resolution image ofZnSe/GaAs interface.

FIGS. 16A-16B depict cross-sectional (FIG. 16A) and top surface (FIG.16B) SEM images of OP-ZnSe grown heteroepitaxially on OP-GaAs templates.

FIGS. 17A-17B depict top surface SEM images of heteroepitaxial growth ofGaSe on a GaP substrate (FIG. 17A) and GaSe on a GaN substrate (FIG.17B) compared to the homoepitaxial growth of GaSe on a GaSe substrate(FIG. 17C).

FIGS. 18A-18E depict SEM top surface image of heteroepitaxial growth ofGaSe on a (100) GaAs substrate in two different magnifications (FIG.18A); SEM cross section SEM image of the same GaSe/GaAs sample (FIG.18B); EDS study of the top GaSe surface clearly indicating presence ofnearly equal amounts of Ga and Se, i. e. that the grown layer is GaSe(FIG. 18C); and, Omega/2Theta XRD scan indicating high crystallinequality of a cubic phase zinc blende gallium selenide Ga₂Se₃ (FIGS. 18Dand 18E).

FIGS. 19A-19B depict Nomarski cross sectional optical image ofGaAs_(0.34)P_(0.66) ternary grown on a 4-degree “off axis” (100) GaPsubstrate (FIG. 19A); XRD (004) peak (blue curve) along with asimulation fit (red curve) was used to evaluate the crystalline qualityof the material and extract the alloy compositional values (FIG. 19B).

FIGS. 20A-20B depict Linear IR transmission of GaAs_(x)P_(1-x) ternarieswith two different compositions compared to the linear IR transmissionof the parenting, GaAs and GaP materials (FIG. 20A); Nonlinear Z-scanshowing that the GaAs_(0.34)P_(0.36) ternary exhibits a lower linearitythan the parenting materials, GaAs and GaP (FIG. 20B).

FIGS. 21A-21F depict Nomarski optical image of a cross section of athick HVPE growth of OP-GaAs_(0.34)P_(0.66) ternary on an OP-GaAstemplate with a pattern period of 43 μm (FIG. 21A); Nomarski opticalimage of a cross section of a thick HVPE growth of OP-GaAs_(x)P_(1-x)ternary (different x-composition) on an OP-GaAs template with a patternperiod of 34 μm (FIG. 21B); A small spot from the image in FIG. 21B at alarger magnification (FIG. 21C); A portion from the upper part of FIG.21B revealing excellent domain fidelity but rougher surfacemorphology—the growth was performed on an OP-GaAs template prepared bythe standard MBE assisted polarity inversion technique with invertedlayer which was finished-up with the growth of a thin MBE encapsulatedlayer (FIG. 21D); Similar area from a growth on an MBE assisted OP-GaAstemplate, where the deposition of the encapsulating layer is omitted,i.e. the HVPE growth is performed directly on the inverted layer showingmuch smoother surface morphology (FIG. 21E); Top surface of the grownstructure shown in FIG. 2B taken with a laser scan using stitchingsoftware and showing excellent domain propagation all the way to the topsurface (FIG. 21D)

FIGS. 22A-22B depict phase matching curves for OP-GaAs (FIG. 22A) fortwo pumping wavelengths, 1.06 μm and 1.55 μm compared to the phasematching curves for OP-GaP (FIG. 22B) and OP-ZnSe (FIG. 22C). Bycomparing the figures one can easily see that to achieve the same outputwavelength (see y-axis) the domain widths (the coherence lengths) ofpatterns on the OP-GaP and OP-ZnSe templates should be 2-3 times larger(see x-axis) than in the case of OP-GaAs, which strongly facilitate theHVPE growth on them.

FIG. 23 depicts the dependence of the growth rate on the chemicalcomposition x during the growth of GaAs_(x)P_(1-x) ternaries. As one cansee when the composition x is closer to a binary material, GaAs or GaP,the growth rate is faster (with the trend GaAs to grow, generally,faster than GaP) but drops down for the compositions in the middle.

FIGS. 24A-24B depict SEM of the top surface (FIG. 24A) and the crosssection (FIG. 24B) of a Si-wafer that was in-situ pretreated in amixture of H₂Se+Hz prior performing a HVPE growth of GaP on the wafer.Both images clearly show that H₂Se strongly attacks the Si-surface,creating numerous randomly distributed etch pits with random shapes anddepth, which hopefully facilitate the initial nucleation of the GaPlayer.

FIGS. 25A-25D depict Nomarski optical images of the top surface (FIG.25A) and the cross section (FIG. 25B) of a GaAs/GaAs homoepitaxial HVPEgrowth; and the top surface (FIG. 25C) and the cross section (FIG. 25D)of a GaAs/GaP heteroepitaxial HVPE growth. Both growths are performedfor one hour at the same growth conditions. However, it is obvious thatthe heteroepitaxial growth provides faster growth rate and smoothersurface morphology.

FIG. 26 presents some nonlinear optical materials that are suitable forfrequency conversion devices along with their most important materialcharacteristics for such applications.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the sequence of operations as disclosedherein, including, for example, specific dimensions, orientations,locations, and shapes of various illustrated components, will bedetermined in part by the particular intended application and useenvironment. Certain features of the illustrated embodiments have beenenlarged or distorted relative to others to facilitate visualization andclear understanding. In particular, thin features may be thickened, forexample, for clarity or illustration.

DETAILED DESCRIPTION OF THE INVENTION

A process for thick heteroepitaxial growth of semiconductor materials ispresented below. The semiconductor structures of the growing layer(s)may be deposited in a horizontal or vertical direction, on plainsubstrates or on patterned templates, including orientation-patternedtemplates.

A further embodiment of the invention states that the heteroepitaxialgrowth is preceded by an in-situ pre-growth treatment of the substrateor the template followed by at least 300-500 μm thick heteroepitaxialgrowth of one or more doped or undoped semiconductor materials or theirbinaries, ternaries, or quaternaries. (Note: An exception of thethickness range is when the purpose of the growth was growth oflow-dimensional (LD) materials. In this case, thicknesses in the rangeof several nm to several μm are acceptable.)

In order to be successful, each separate heteroepitaxial combinationmust meet particular requirements, including the lattice mismatch andthe accumulated strain. Accordingly, the heteroepitaxy exhibited in anyparticular example below will be based on the degree and the sign of thelattice mismatch between substrate and growing layer, as well as on howthe strain accumulated in the growing layer because of the lattice andthermal mismatch is released—in plastic or elastic strain releaseprocesses. While the elastic strain release process occurs throughsurface roughening, a typical example of a plastic strain releaseprocess is the periodic formation of the so-called “misfit dislocations”(MDs). Such dislocations may appear after a certain critical thicknessh_(c) of the so-called “pseudomorphous growth”, during which the layeris “forced” to grow with the lattice constant of the substrate. (Note:The words “mismatch” and “misfit” are almost identical, but theirmeanings are distinct in this context. However, in particular cases, onewill be preferred to the other. For example, it is proper to say“lattice mismatch” and “misfit dislocations”.) In this invention, weteach that the sign and the degree of the lattice mismatch and theperiodicity of the MDs may be used as criteria for one to determine inadvance how successful a new case of heteroepitaxy would be.

The lattice mismatch ƒ_(%) is calculated using the formula:

$\begin{matrix}{{f_{\%} = \frac{b_{o} - a_{o}}{a_{o}}} \cdot 100} & \left( {{eq}.1} \right)\end{matrix}$where a₀ and b₀ are the lattice constants of the substrate and the layermaterial. The lattice constants of some traditional semiconductormaterials are presented in FIG. 1 , which shows their bandgap energiesas a function of their lattice constants. From FIG. 1 , one can easilysee that some materials, although having different bandgap energies,have close lattice constants and could be suitable for heteroepitaxy.Such are, for example, GaP and Si, ZnSe and GaAs, AlAs and GaAs, ZnTeand GaSb, ZnS and GaP, or ZnS and Si, etc.

The periodicity τ of the misfit dislocations is determined by:

$\begin{matrix}{\tau = \frac{100}{f_{\%}}} & \left( {{eq}.2} \right)\end{matrix}$

As an example, we can determine the lattice mismatch ƒ_(%) and theperiodicity of the MDs τ in the particular heteroepitaxial case ofgrowth of GaP on a GaAs substrate. The lattice constant (a_(o)) ofGaAs=5.6532 Å, while the lattice constant (b_(o)) of GaP=5.4512 Å.According to equations (1) and (2), in this example the lattice mismatchƒ_(%) is negative (−3.57%) because b_(o) GaP<a_(o) GaAs; we shouldexpect the appearance of MDs at a periodicity τ of about 28 (i.e.100/3.57) interatomic distances. Such lattice mismatch (−3.57%) may beconsidered as large. In general, lattice mismatches of 3-4% and more areconsidered as relatively large, while lattice mismatches under 1% may beconsidered as relatively small. Thus the lattice mismatch between GaPand GaAs (−3.57%) may be considered as large, while the lattice mismatchbetween ZnSe and GaAs (+0.26), for example, may be considered as small.However, whether a particular mismatch can be considered as large orsmall, it depends on other factors as well, for example, on the strengthof the bonds (the bond dissociation energies) between the atoms of thesubstrate and those of the growing layer. For example, (Table 1) thebond energies of the bonds Ga—As and Ga— P are in the same order ofmagnitude. This means that the As and P atoms can easily replace eachother, forming an intermediate GaAsP ternary transition layer betweenthe substrate and the growing layer. Namely, because of this GaP andGaAs can grow successfully on each other even at the larger mismatch of3.57%. As we discovered in the course of our study the formation of thisintermediate ternary layer could be initiated still during thepreheating stage of growth by treating the substrate with its non-nativeprecursor, i.e. by exposing GaAs to phosphine (PH₃) or GaP to arsine(AsH₃). As Table 1 also shows, from this point of view GaSb, InSb andInP are also “easy” substrates due to the low bonding energies of theiratoms. However, as one can see from Table 1, due to the high bondingenergy of the Ge—Ge bond and, especially, of the Si—Si bond, thesecommon substrates are hardly treatable. Thus, in the case of growth ofGe/Se, for example, namely because the atomic bonds are strong in bothmaterials, the lattice mismatch of +3.96% between Ge and Si isconsidered as huge, no matter that as a number this mismatch is not muchdifferent from the lattice mismatch between GaAs and GaP:

TABLE 1 Some bond dissociation energies (standard state enthalpychanges) at T = 298 K. Bond dissociation energy Bond AHf₂₉₈ [kJ/mol]Ga—As 209 Ga—P 230 Ga—Sb 209 In—Sb 152 In—P 198 Ge—Ge 274 Si—Si 327

The sign of the lattice mismatch, minus (−) or plus (+), is alsoimportant. For example, it was determined that the thickness of thepseudomorphous growth, i.e. the critical thickness h_(c), is larger whenthe lattice mismatch is negative and the film is growing under tensilestrain than in the case of a positive lattice mismatch when the layer isgrowing compressively strained. To clarify again that, according to eq.1, we have a negative mismatch and a layer growing under tensile strainwhen the lattice constant of the layer material is smaller than thelattice constant of the substrate. In contrast, a positive mismatchmeans a larger lattice constant of the layer material—a case when thelayer is growing under compressive strain. The significant difference inthe mechanisms of dislocation nucleation (after the moment in which thepseudomorphous growth becomes energetically unfavorable and theaccumulated elastic strain must be relieved somehow) in the case oftension vs. compression contributes to this difference as well. Forexample, while in the compression case the dislocations nucleate bysqueezing out an atom at the base of surface depressions, in the tensioncase, the nucleation of misfit dislocations involves the concertedmotion of a relatively large number of atoms, leading to insertion of anextra lattice (plane) row into an already continuous film. In additionto all that, the film morphology depends intimately on the sign of themisfit (+ or −), i.e., on the type of the strain (tensile orcompressive). It is experimentally confirmed, for example, that growthunder tensile strain (negative misfit) favors 2D growth, which usuallyresults in smooth surface morphology, while compressive growthfacilitates 3D growth, which typically results in hillock type, i.e.,rougher surface morphology. In other words, plastic relaxation (negativemisfit, tensile strain) is encouraged when the goal is to growmetamorphic buffers, while elastic relaxation (positive misfit,compressive strain), being associated with surface roughening, shall beused to drive quantum dot self-assembly processes. All this is, again,in support our notion that the growth under tensile strain, as it is inthe case of growth of GaP on GaAs (negative misfit), should be morefavorable for our coals than the opposite case of growth of GaAs on GaP(positive misfit).

The linearly increasing elastic strain accumulated during thepseudomorphous growth must be released at a certain point. The formationof MDs (misfit dislocations) is one of the possible mechanisms of strainrelief. However, deeper crystallographic considerations are necessary todetermine where they should be expected, or on which crystallographicplane it is most probable for the MDs to appear. In a zinc blendestructure (this is the structure of many of the compound semiconductormaterials presented herein, e.g. GaAs, GaP, ZnSe, etc.), for example,the biaxial strain 6 accumulated during pseudomorphous growth may beresolved (see FIG. 2A) into a uniaxial shear stress τ on the (111)dislocation glide plane. At the same time, the directions of σ and τ, ofcourse, will be opposite depending on whether the layer is growing undertensile (negative mismatch) or compressive (positive mismatch) strain,i.e. whether the lattice constant of the growing layer is smaller orlarger than the lattice constant of the substrate. Thus, recalling thatthe accumulated strain may be released in either elastic (surfaceroughening) or plastic (dislocation nucleation) relaxation processes,one may assume that in the latter case the most probable plane where themisfit dislocations shall appear is (111). Such dislocations were indeednoticed in the (111) zone in the particular case of GaP/GaAsheteroepitaxy as the TEM image in FIG. 2B indicates. However, they donot appear around the theoretically predicted critical thickness of thepseudomorphous growth but in a later stage of the growth, which tells usthat during the fast growing HVPE process other mechanisms may alsocontribute to the strain relief. According to some cross-sectionalhigh-resolution TEM images, which will be discussed in detail later inthe text, roughening surfaces, formation of voids, and othercompositional variations observed near the GaP/GaAs interface may serveas an alternative strain relief mechanism. These energy absorbing eventsmay postpone the formation of the MDs until a later stage of growth, oreven entirely replace it. All this provided some insight that it mightnot be terribly detrimental if the surface of the substrate was to bemade rougher with the intention of facilitating the initial layer'snucleation. As for the top surface of the grown layer, for frequencyconversion we need optically transparent cross sections for thepropagating waves to go through and not a smooth layer surfacemorphology. Fortunately, after the first several microns of highlydefective area (FIG. 2B) the transparency of the layers improves withincreasing thickness, similar to many other material cases. The reasonsfor this “self-improvement” could be many but, in general, growth ofthicker layers is, itself, a way for reducing the treading dislocations,because with the thickness increases the probability increases for twoopposite treading dislocations to fall within their interaction cutoff(eventually annealing each other) as well.

Roughening of the surface may be the result of exposing the substrate toa non-native precursor during the preheating stage. This is supported byFIGS. 3C-3D, which present an SEM image (FIG. 3C) and an AFM image (FIG.3D) of a GaAs substrate preheated for 1 h in a PH₃:H₂ atmosphere. It isworth to mention that the damages (pitting) are about the same afterpreheating the GaAs substrate for 1 hour in PH₃:H₂ atmosphere and for 1minute only, so they occur quickly.

FIG. 3A presents an SEM image of a GaAs substrate preheated for 1 h inAsH₃:H₂ atmosphere, according to an embodiment of the invention; one cansee that such roughening (see FIGS. 3C and 3D) never occurs when thesubstrate is exposed to its native precursor (see FIG. 3A) during thepreheating stage. However, although the temperature is still lower thanthe deposition temperature, some thermal decomposition of the substratemay occur if the GaAs substrate is preheated only in an Hz atmosphere,as shown in FIG. 3B. That is why, to prevent the thermal decompositionduring growths of GaAs or GaP the wafers should to be exposed to anAsH₃:H₂ (for a GaAs wafer) or a PH₃:H₂ (for a GaP wafer) mixture oncethe furnace temperature achieves 350-400° C., even though thedecomposition temperature is much higher—about 700° C. Preheating thesubstrate only in Hz, for example, actually results in an intensiveevaporation (and shortage) of the more volatile Group V-atom (As or P inthe particular cases of GaAs or GaP) (see FIG. 3B). Going further inthis direction by pretreating the GaAs substrate in phosphine (PH₃), orin a PH₃:H₂ mixture, leads to severe pitting of the GaAs surface (seeFIGS. 3C, 3D, 4A, and 4C). Similarly, preheating the GaP substrate inAsH₃ or in an AsH₃:H₂ mixture resulted in even more severe pitting ofthe GaP surface (see FIG. 4B and FIG. 4D). Even with the time ofexposure as short as 1 minute, the visible surface damage on thesubstrate's surface will be about the same as after one hour of exposureof the substrate to the nonnative precursor (as shown in FIGS. 3C-3D and4A-4D).

It is thought that the stronger influence of AsH₃ on GaP than of PH₃ onGaAs (compare the ranges of the distances between peaks and valleys onthe scales that are left from FIG. 4A and FIG. 4B) should be attributedto the lower surface quality (i.e. the higher EPD) of GaP, which makesthe surface more vulnerable to the AsH₃ attacks. However, to fairlycompare this effect we must also consider the differences in the thermaldecomposition of GaAs and GaP, as well as the differences in the thermaldecomposition of AsH₃ and PH₃. It is known, for example, that theAs-vapor pressure over a GaAs surface is lower in comparison to theP-vapor pressure over GaP, which means that GaP decomposes faster or toa greater extent than GaAs. At the same time, the thermal decompositionof PH₃ and AsH₃ over a GaP substrate or, respectively, over a GaAssubstrate in the temperature range of 400-600° C., (see the left side ofFIG. 5 ), are nearly equivalent, but still slightly in favor of the AsH₃decomposition under 500° C. However, according to the right side of FIG.5 , the AsH₃ decomposition over a quartz surface (the surface of ourreactor tube) within the pretreatment temperature range, i.e. above 350°C. but less than the growth temperature, is significantly stronger thanthe thermal decomposition of PH₃. Thus, still during the preheatingstage, due to the stronger decomposition of AsH₃, there will be plentyof arsenic (As) atoms in the AsH₃, which is overflowing (i.e. flowingover) the GaP substrate. At the same time, with increasing substratetemperature, the GaP will decompose more and more, losing morephosphorus (P) atoms which can be easily replaced in the crystal cell bythe liberated As atoms from the decomposing arsine. That is why AsH₃attacks more GaP severely, which results in deeper and more intensivepitting—see FIG. 4B) than when PH₃ attacks the GaAs surface (see FIG.4A).

It was discovered that surface roughening (looking like pitting) is notonly the result of exposing the semiconductor material to a non-nativeprecursor during the preheating stage. Elemental analysis performed byElectron Dispersion Spectroscopy (EDS) of surfaces exposed to non-nativeprecursors (see FIGS. 6A-6C) indicated that exposing, for example, GaAsto PH₃ or to the aforementioned PH₃-containing mixtures (PH₃:H₂ orAsH₃:PH₃:H₂) provokes the formation of ternary GaAs_(x)P_(1-x) islandsduring the preheating stage prior to initiating the heteroepitaxialgrowth of GaP/GaAs. These islands eventually coalesce in a later stageof growth forming a continuous intermediate transition GaAs_(x)P_(1-x)buffer layer (FIG. 7A and FIG. 7B). By absorbing some of the mismatchstrain, this transition buffer layer helps to accommodate the growinglayer to the foreign substrate, realizing a smooth transition betweenthe substrate to the growing material. Exposing GaP to the relatednon-native precursor AsH₃ or their mixtures (AH₃:H₂ or PH₃:AsH₃:H₂) ledto similar results.

The effect that the non-native precursors may have on the GaP and GaAssubstrates (see FIG. 4A and FIG. 4B) is not a single, isolated case.This approach works well in many more material cases (see FIGS.13A-13B). Accordingly, this provides the opportunity to growmulti-layered multi-material heterostructures (see FIG. 8 ) in which,depending on the pursued application, two or more materials may byalternated multiple times after achieving certain thicknesses within thesame heterostructure in the frame of one continuous growth process. Forexample, we may start the growth by growing GaP on a GaAs substratepretreated in phosphine or in a PH₃:H₂ mixture. Then, after preheatingthe already grown GaP layer in arsine or in an AsH₃:H₂ mixture, tocontinue with the HVPE growth of GaAs. After this second step, we maychoose to preheat the already grown GaAs layer in hydrogen selenide(H₂Se) (or an H₂Se:H₂ mixture) following by HVPE growth of ZnSe/GaAs,etc. Such structures, with the ability to cover large portions of thespectrum, may have applications that will cross known boundaries—thealready mentioned portable highly-efficient solar cells, multiphotondetectors, laser sources (including frequency conversion sources) thatsimultaneously cover both atmospheric windows of transparency between2-5 and 8-13 μm, etc. Finally, involving common substrates such as Simay open many doors in optoelectronics, resulting in cost reduction ofthe final products in all known areas where Si is involved.

The proposed approach is to some extent universal because it may beapplied to many different materials deposited one over another in aone-step epitaxial process, with or without the intentional assistanceof an intermediate sub-lattice transition buffer layer (see FIGS. 7A-7B)deposited between them. However, such a layer may facilitate the growthof the following heterostructure. Quality control is crucial. First, thetemperature at which the non-native precursor (or mixture) will beintroduced in the reactor must be carefully chosen, as well as theratios of the precursors' mixture, i.e. the mixture of the native andnon-native precursors, their flow rates, the reactor pressure, etc. Onemay also choose to gradually change over time the ratio of thenon-native/native precursor gasses in the mixture in order to build-up agraded buffer layer, i.e. a layer with a gradually changing composition.The purpose of this is, in order to match the lattices more closely, wemay start by growing the substrate material and end up by growing thelayer material. Thus, as an example, if we are planning a growth of GaPon GaAs, the process may start with maintaining the GaAs substrate in anAsH₃:H₂ mixture to protect its surface from thermal decomposition.Later, we may gradually start introducing PH₃, and increasing its amountin the mixture AsH₃:PH₃:H₂, while gradually reducing the amount of AsH₃to zero. This process provides the conditions for growing the desiredintermediate transition GaAs_(x)P_(1-x) ternary buffer layer, in whichthe chemical composition changes gradually to achieve a balanced growthof a pure GaP layer. Although HVPE is a relatively fast growth process,this invention disclosure provides procedures for a gradual change inthe lattice constant with a precise control of both the composition andthe thickness of the buffer layer for the sake of achieving a smoothtransition between the substrate and the growing material. In contrastwith other known techniques, the process proposed here for buffer layerdeposition is an in-situ step, inseparable from the entire growthprocess. Starting with the formation of the buffer layer by exposing thesubstrate to a non-native precursor (or to a mixture ofnon-native/native precursors), this process combines features of themajor techniques for buffer layer engineering. Such are: building agraded layer; growing a ternary layer from (or not from) the parenting(substrate and layer) materials; growth on a patterned template—in ourcase the pattern consists in different sized, randomly distributedternary islands; and using the highly defective areas of the bufferlayer for efficient strain relief.

Because it is capable of controlling the thickness of the buffer layer,this invention allows one to extend the idea of the deposition of aternary transition buffer layer to the growth of ternary layers hundredsof microns thick. This may be achieved by maintaining the ratio of themixture of the native and the non-native precursors constant, which willensure achieving the desired composition (x) in the growing ternary andkeeping it constant during the entire growth process. As an example, thedisclosed process has been used to grow up to 300 μm thickGaAs_(x)P_(1-x) ternary layers on both GaAs and GaP substrates at therelatively high growth rate of about 100 μm/h. The ability to grow thickternaries by the proposed process is important because the tailoring ofdifferent compositions allows one to achieve the best combinations ofproperties, which may be suitable for a particular application. Forexample, it was discovered that in the particular case ofGaAs_(x)P_(1-x) the following composition GaAs_(0.34)P_(0.66) (x=0.34)provides lower two-photon absorption (2PA) than the 2PA of GaAs buthigher nonlinear susceptibility than GaP in the wavelength of interest(1-1.7 μm); these parameters are of great importance for applicationssuch as QPM frequency conversion. Another example is that by changingthe x-composition of the GaAs_(x)P_(1-x) ternary one may “tune” itsbandgap energy to an optimal value that fits to the bandgap of Si in adual junction solar cell panel made of the ternary with Si. This ideamay be applied to other ternaries in heterostructures with Si or withother common substrates.

Thus, such a combination of material properties satisfies therequirements for using this new ternary material for frequencyconversion devices as well as for many other applications. At the sametime, ternaries may be grown on either one of the parenting materials(in this case on GaAs or on GaP substrates) depending on how close tothe given substrate is the ternary composition. For example, in the casewhere the content of As is more than the content of P in the ternary,GaAs will match closer as a substrate, while in the opposite case GaPshall be the more suitable substrate.

Because of the smaller lattice mismatches that the ternary(GaAs_(x)P_(1-x)) has with each of the two substrates (GaAs and GaP)compared to the lattice mismatch between the original materials (GaP andGaAs) the growth of ternaries is also an easier, more favorable,heteroepitaxial task.

Modification of the material properties, as was already mentioned, isanother opportunity that the proposed invention provides and theaforementioned examples demonstrate the usefulness of such modificationsfor the development of new frequency conversion devices, e.g. for lasersources in the case of using GaP, GaAs, and their GaAs_(x)P_(1-x)ternary. However, other material combinations may provide thick growthsof other ternaries or quaternaries that may result in products thatcould support other research and development fields, e.g.optoelectronics, sensing (detectors), solar cell industry, etc.

This invention also allows to use the exposure of the substrate, the OPtemplate, or the already grown OP material to a non-native precursor asan easy way to determine the crystal polarity of the material and, fromhere, to use this technique for polarity control during both thefabrication of the OP templates and the subsequent thick HVPE growth onthem. This is possible because, in contrast to the case where thesubstrate is exposed to a non-native precursor and the shape of theobserved pits are irregular and randomly distributed, in the case ofexposing an OP template to a non-native precursor the shape of the pitsare rather longitudinal. They are also predominantly oriented in twomutually perpendicular directions on the surface of domains withopposite crystallographic orientations (opposite polarity).

FIG. 9A and FIG. 9B, for example, present an area around the boundarybetween two oppositely oriented domains, (100) and (TOO), of an OP-GaAstemplate before and after preheating the OP-GaAs template in thepresence of PH₃. FIG. 9C and FIG. 9D present the outlined small areasfrom FIG. 9B at higher magnifications. As one can see in FIG. 9C andFIG. 9D, after exposing the template to PH₃, the pits on the treatedOP-GaAs template are longitudinal and tend to be oriented in twomutually perpendicular directions, along [011] and along [011], on the(100) and (100) oriented domains. This phenomenon, from a practicalpoint of view, is an important feature of this invention, because itgives us a tool to easily determine the presence of the opposite domainorientations on the OP-template. Moreover, this approach is also an easyway to estimate the quality of the OP-template prior to the growth, orthe quality of the growth on the template QPM structure, which is asimple in-situ or post-growth non-destructive evaluation step. Untilnow, it was possible to determine crystallographic orientations onlywith great uncertainty. The estimation was based on the type of thesurface texture or the specific shape of grown surface features thatwere experimentally associated more or less to one orientation oranother. One may also judge the crystallographic orientation by the rateof etching (which is usually different for different crystallographicdirections) or by the shape of the etch pits revealed after etching thesample. Etching, however, means damaging the surface, after which thesurface is not usable for the subsequent thick HVPE growth.Heteroepitaxial growth, performed on OP-GaAs templates exposed to anon-native precursor (PH₃), resulted in thick (up to 500 μm) highquality OPGaP with rectangular domains having excellent fidelity (seeFIG. 9E). Depending on the type of the material, the domain width, andthe pump wavelength, such QPM structures may be used for frequencyconversion in, practically, any part of the spectrum. This includesfrequency ranges which are uncovered or poorly covered by laser sources,which means realizing new practical applications that may easily exceedeven the bravest expectations. For example, devices based onIII-Nitrides with their ability to radiate in the UV and the close to UVvisible spectrum could be engaged in water purification, energyconservation, high power lasers for high-energy physics, etc. Frequencyconversion sources based on wideband semiconductors such as GaAs, GaP,ZnSe, GaSe, ZnTe, etc., however, radiate in the mid and longwave IR.They, especially, if they cover the two atmospheric windows oftransparency, could find applications in the IR countermeasures (IRCMs)to protect aircraft and ships from heat seeking or laser guidedmissiles, in enhanced laser radar systems (distance detection and targetrecognition), or in long-range ultra-fast reliable IR communications.Respectively, FC (frequency conversion) sources radiating in themicrowave and/or THz regions may be useful in airport scanners, remotesensing and spectroscopy of chemicals (explosives) or biological agents,in industry (automotive pedestrian protection systems), medicine (breathanalysis, biopsy-free cancer cell detection), and science (ultrafastspectroscopy of chemical reaction dynamics).

As already explained above, the proposed process may be used for thegrowth of metamorphic buffer layers or for the formation of quantumdots, quantum wells, or other nano- and micro-structures. This dependson which mode of heteroepitaxy is stimulated during growth: Volmer-Weber“island growth”, Frank—van der Merwe “layer-by-layer growth”, or theStranski-Krastanov “layer-plus-island growth. In other words thisdepends on the sign and the magnitude of the of the lattice mismatchand, from there, the type of elastic (tensile or compressive) strain,and the mechanism of strain relief—elastic (surface roughening) orplastic (dislocation formation). By skillful use of these growth modesthis process may combine similar or different materials, e.g. commonelectronic materials, e.g. Si or Ge, with some linear and nonlinearoptical materials, e.g. GaAs, GaP, GaSe, ZnSe, ZnTe, ZnS, etc., or evenwith their ternaries or quaternaries. Thus, the described approachcontributes to advances in the development of optoelectronic devices aswell.

The disclosed process allows for one-step thick growth without the needfor a preliminary deposition (usually using a thin growth technique) ofanother material with a smaller lattice mismatch with the growingmaterial and/or with the substrate. For example, as it is known in theprior art, thick HVPE GaN layers can be grown on SiC substrates onlyafter the deposition of a thin AlN layer by MBE or MOCVD. Similarly,thick HVPE GaN may be grown on thin GaN or AlN deposited in advance onsapphire, again, by MOCVD or MBE (this was already discussed in moredetails above). The MBE and MOCVD on one hand, and the HYPE on the otherare growth processes, which are quite different by their nature. Thus,while the first two (MOCVD and MBE) are far-from-equilibrium processes,the third one, HVPE, is a close-to-equilibrium process. This makes theMOCVD and MBE “less sensitive” to lattice mismatches than HVPE. However,although MOCVD and MBE can “handle” heteroepitaxial growths, in general,at larger lattice mismatches, they, in contrast to HVPE (which is atraditional technique for hundreds of microns of thick growth), can beused only for, typically, 1-2 μm thin growths. This means that the oldapproach of thick heteroepitaxial growth, using as a first step MOCVD orMBE and after that HVPE, is a two-step growth process which needs morehigh-tech instruments and more equipment, i.e. greater investments.These limitations are not necessary with the disclosed approach, whichfocuses on the use of only HVPE.

The disclosed process also eliminates the need to grow (typically byHVPE) an intentionally deposited low temperature (LT) buffer layer onthe substrate prior to the growth of the high temperature (HT) layer.This is known for the thick HVPE growth of GaN on a sapphire substrate,for example. The deposition of such intermediate transition layers aimsto reduce the strain between the sapphire substrate and the growing GaNlayer. The LT buffer layer can do this job, i.e. to accommodate thegrowing layer to the substrate. At the same time, however, the LT bufferlayer is a highly defective area, a layer with extremely low crystallinequality and, thus, it is a source of a great number of different defectssuch as, for example, treading dislocations. All this means that the LTbuffer layer does not provide always an optimal foundation to start thegrowth of the actual HT GaN layer. The proposed approach allows theformation of an intermediate transition layer naturally, in-situ, duringthe initial stage of preheating the substrate, and not through a growthprocess—it occurs prior to the start of growing the actual layer butalso may continue during the initial stages of growth as well. Accordingto the present invention, it is not necessary for the buffer layer to bea LT layer. Instead, the choice of the temperature of the buffer layerformation may be controlled, and thus its quality may be controlled.

We would like once again to emphasize another significant differencebetween the proposed buffer layer growth and the prior art by using thesame example: an HVPE-grown LT GaN buffer layer. In the prior art caseone may choose to change the V-III ratio (i.e. the ratio between thecontent of Ga and N) during the buffer layer deposition in order forthis layer to accommodate both the substrate and growing layer. However,although these changes may change some material properties, like thebalance in the carrier concentration, they may not provoke significantchanges in the lattice mismatch and thus may not contribute much toaccommodating the buffer layer (GaN) and the foreign substrate (SiC).Moreover, they not only may not help much in the buffer layer/substrateheteroepitaxy, but may aggravate the subsequent layer/buffer layerhomoepitaxy. In summary, since the buffer layer and the subsequent layerare still from the same material, GaN, as a practical matter, we performheteroepitaxy only in regards to the substrate (SiC or sapphire), whilethe HT GaN layer still grows homoepitaxially on the LT GaN buffer layer.In contrast, the inventive method, disclosed herein, is aheteroepitaxial growth of a buffer ternary layer (GaAsP in the chosenexample) concerning both the substrate (GaAs) and the growing layer(GaP), since the lattice constant of the ternary (GaAsP) is alwaysdifferent from the lattice constants of the substrate and the growinglayer. As an option, its composition may be continuously, graduallychanged during the preheating stage but this may also continue duringthe initial stage of growth for a gradual replacement of the substratematerial with the growing layer. This means that at the beginning thelattice constant of the buffer material is closer to the latticeconstant of the substrate material, while at the end of its depositionthe lattice constant of the ternary material is already close to thelattice constant of the layer material that will be grown on the ternarybuffer layer (which means changes in the buffer layer composition makesense). However, there is another significant difference. In this casewe do not change the V/III ratio of the material of the buffer layer,but only the ratio between the V-group atoms in the ternary, which areAs and P in the given example. In addition, in the same example theternary GaAsP is a combination of the two parenting materials—thesubstrate (GaAs) and the layer (GaP) material. However, this is not astrict requirement of this disclosure. The intermediate transitionternary layer may be from any suitable materials that accommodate thegrowing layer to the substrate. For example, if growth of GaSe on Si isattempted and the suggested non-native precursor, hydrogen selenide(H₂Se), does not “pretreat” the Si substrate properly, anothernon-native precursor (for example PH₃) may do a better job, at the sametime forming on the Si surface an intermediate layer (GaP) with whichGaSe has a fairly small lattice mismatch. All these options makes theproposed approach much more flexible than the approaches for growth of atransition buffer layer used until now.

Thus, the optimized growth approach presented herein avoids or solvesmany of the current problems and shortcomings of heteroepitaxy. Theoptimized growth approach presented herein demonstrates severaladvantages over the known and comfortable homo- and heteroepitaxialprocesses. The disclosed process clearly indicates that there are manyparticular cases when heteroepitaxy, as stated here, may be preferableeven when homoepitaxy is possible.

Heteroepitaxy provides economic and quality advantages: for example, theGaP wafers (for 2-inch wafers) available on the market is 5-6 times moreexpensive than the corresponding GaAs. In addition, the commerciallyavailable GaP wafers have much lower quality with respect to the etchpit density (EPD) and wafer parallelism. This means that the quality ofOP-GaP templates prepared from such wafers will also be low, and that iswhy we should expect poor quality of the HYPE growth on them.Accordingly, the performance of frequency conversion devices based onsuch templates will also be unacceptable, because of the expected poordomain fidelity. The ability to use GaAs substrates and OP-GaAstemplates for growth of GaP and OP-GaP solves this problem.

In addition, heteroepitaxy, as stated in this disclosure, enables theuse of techniques suitable for thick epitaxial growth, e.g. HVPE, andthe corresponding practical applications that require thick epitaxialgrowths. At this moment, due to the complex growth mechanisms ofheteroepitaxy, knowledge of such mechanisms is relatively limiteddespite the great deal of effort made over the last couple of decades.For example, on an atomic scale it is known how the growth proceeds onlyfor the first few monoatomic layers, even for the homoepitaxial growthof only a few plain semiconductors, e.g. Si and Ge. That is why thesemiconductor industry has adopted primarily thin growth techniques suchas MOCVD and MBE, and only for a limited number of well-studiedmaterials.

The disclosed heteroepitaxial approach relies on the most promisingcandidate for thick epitaxial growth, the HVPE technique. Some otherexisting techniques for thick growth are more bulk-growth thanlayer-growth techniques, and each of them suffers from its owndisadvantages. For example, the aforementioned PVT process, usedsuccessfully in the industry for SiC bulk growth, continues to havematerial quality issues. This is, namely, the reason for seekingalternative approaches for the growth of SiC such as, for example, theTop Seeded Solution Growth (TSSG). PVT (and in some cases the Bridgmanmethod) is the method of choice for the growth of other materials,already mentioned in the text, as well. Such materials include GaSe,ZnSe, ZnTe, ZnS, etc. However, looking at what is available on themarket, one can easily figure out that the larger offered samples fromsuch materials are either polycrystalline, or if they are crystalline,they are not large enough for device development. In addition,typically, they still consist of several domains with differentcrystallographic orientations, i.e. they are still not exactly“crystalline”. PVT has been used for the heteroepitaxy of OP-ZnSe onOP-GaAs templates, but the grown OP-ZnSe structures yielded such limitedoptical results that any further attempts in this direction werediscontinued. Obviously, the PVT, by just mechanically delivering theraw material to the substrate surface, is less controllable than HVPEand incapable of providing the flexible options and the variety ofchemical paths that the HVPE technique provides. The rest of the optionsfor thick growth are even less competitive. For example, liquid phaseepitaxy (LPE) is, practically, a solution growth technique, whichsuffers from numerous limitations, including relatively thin (microns)growths, difficulty in controlling the composition of the buffer layer,and edge effects (low quality of the layer edges, which are close to thecrucible walls, etc. Thus, one of the best achievements of LPE—up to150-200 μm thick GaAs layers, grown in about 3 hours—is still notcomparable with the millimeter thick growth of different materialsdeposited by HVPE with growth rates of up to 300 μm/h. Solvothermalgrowth is another example for thick growth. Although quite successful inthe bulk growth of quartz, this technique has never achieved anythingeven close to that performance with any other attempted materials. Yes,growth can be performed heteroepitaxially on multiple substrates but,once the autoclave is closed, nothing else can be done to correct thegrowth conditions, if necessary. In addition, the grower may wait formonths to gain enough layer thickness on the samples that are still notlarge enough for device development. It was found that HVPE providesmore options for controlling the growth process and more choices forgrowth chemistries for thick homo- and heteroepitaxy. This, however,does not mean that HVPE still does not have its own problems. Such are,for example, the severe parasitic nucleation on the inner quartzsurfaces of the reactor that always accompanies the growth and competeswith the deposition process that occurs on the substrate surface. Suchparasitic nucleation slows down the process (reducing the growth rate onthe substrate), depletes the precursor sources, and deteriorates thelayer quality.

The disclosed process allows successful heteroepitaxial growth even atrelatively large lattice and thermal mismatches, and without patterningthe substrate, which in many cases is the standard procedure. Thepresent invention is based on the accumulation of a significant amountof information about a great number of semiconductor materials andvarious growth processes used to grow them. This allowed us to realizethe significance of the determination of important characteristics ofheteroepitaxy, e.g. the thickness of the pseudomorphous growth, theperiodicity of the misfit dislocations, and the mechanisms of strainrelief, and to successfully make samples for several particular cases.In turn, the determination of these parameters and, in general,enriching our experience and knowledge related to these processesallowed us to develop criteria by which to predict other successfulcases of heteroepitaxy, and thus to realize heteroepitaxial growth atmismatches that at first sight looked impossible. Pseudomorphous growthis not ternary or quaternary growth. Instead, it is the initial stage ofgrowth during heteroepitaxy. During this stage of growth the grown layeris “forced” to grow with the lattice constant of the substrate. Thisgrowth occurs at the expense of building a linearly-increasing strain inthe layer as a result of the lattice mismatch between layer andsubstrate. However, after reaching a thickness called critical thicknessh_(c). the strain starts to be released by different energy absorbingmechanisms, e.g. formation of misfit dislocations, roughening ofsurfaces, formation of voids, etc.

The disclosed method is based on our understanding of the complexchemistry and growth mechanisms of heteroepitaxy of widebandsemiconductor materials. The method secures a smooth transition betweentwo distinct materials, for example GaAs and GaP, or GaAs and ZnSe, orGaP and GaSe, or GaSb and ZnTe, etc., not through a forced-growthprocess but while preheating the substrate and during the initial stagesof growth. During the initial growth stages, the process directs thegradual replacement of substrate atoms, for example V-group atoms, withV-group atoms from the growing material. (Note: The later, however, isnot a strict requirement meaning that the replacing atoms can by notonly V-group atoms of the growing material but also any other suitableatoms that could assist the smooth substrate-to-layer transition). Thusthe process, according to the given example, may direct the replacementof As atoms in the crystal cell of a GaAs substrate with P atoms duringthe preheating process, which may be conducted in a phosphine (PH₃)atmosphere or in the flow of a mixture of phosphine (PH₃) and arsine(AsH₃). The operator may also make timely decisions to optimize theprocess, e.g the temperature (if the growth is still in the preheatingstage) at which to initiate such replacement, i.e. at which temperatureto start exposing the substrate to the non-native precursor), andwhether this temperature should be kept constant during the depositionof this buffer layer, or whether it should be increased at some rateuntil achieving the growth temperature, etc. The user also must decidewhether to keep the arsine/phosphine ratio constant or to graduallychange this ratio from arsine only to phosphine only in order to achievethe smoothest transition between substrate material (e.g. GaAs) andgrown layer material (e.g. GaP). These possibilities point to the greatflexibility of the proposed method in controlling the quality of thebuffer layer.

From another point of view, the disclosed approach is universal alsobecause it may be applied to a wide range of different materials havingwide ranges of differences in their lattice constants and in theirthermal properties expressed by the differences in their thermalexpansion coefficients and their thermal conductivities. In spite of allthese differences, by using this technique, these materials still may bedeposited one over another in a one-step epitaxial growth process, withor without the intentional deposition of the aforementioned intermediatesub-lattice transition buffer layer between them. This approach has beendemonstrated to be extremely successful in the growth of GaP on GaAs andin the opposite case, i.e. in the growth of GaAs on GaP although thesetwo cases, from the perspective of lattice mismatches, are not highlyfavorable (see FIG. 25 ). The disclosed method has been applied to someother related materials systems which, from point of view of latticemismatches, are more favorable than GaP/GaAs. One of these cases is theheteroepitaxy of ZnSe on plain GaAs substrates and on OP-GaAs templates.These growths resulted in smooth layer surfaces and high ZnSecrystalline quality on plain substrates and good domain fidelity whenthe growth was performed on OP templates. Respectively, growths of cubicand hexagonal phase GaSe were also performed on plain GaP, GaAs, Si, andGaN substrates. The initial results, especially in the case ofGaSe/GaAs, are promising. However, a long line of other favorableheteroepitaxial cases with small lattice mismatches such as ZnTe/GaSb,ZnS/GaP, GaP/Si, etc. (see FIGS. 1 and 13A-13B, and Table 2) are in theplan to be explored in the near future in order further to confirm thefeasibility of the proposed method.

Regarding the particular case of the growth of ZnSe on GaAs, the GaAssubstrate (or template) is preheated in hydrogen selenide (H₂Se) mixedwith Hz or in a H₂Se:AsH₃:H₂ mixture in order to partially and graduallyreplace the V-group atom (As) in the GaAs crystal cell with Se (which isa VI-group atom) and thus form a GaAs_(x)Se_(1-x) ternary buffer layer.After this step, the growth may continue with the introduction of theZn-precursor, which may be either metallic Zn overflowed by HCl (or anHCl+H₂ mixture) to form zinc chloride (ZnCl₂), or simply ZnCl₂overflowed by Hz, or even a Zn-rich ZnCl₂ solution overflowed by HCl+H₂mixture. (Note: The latter one may be the better choice due to therelatively high vapor pressure of zinc.) Table 2 compares the latticemismatch of the realized GaP/GaAs heteroepitaxy with the latticemismatches of some other examples (incl. ZnSe/GaAs) for prospectiveheteroepitaxial cases as more examples and details are provided in FIGS.13A-13B).

TABLE 2 Some favorable cases of heteroepitaxy based on their latticemismatch. Heteroepitaxy Lattice mismatch [%] GaP on GaAs −3.57 ZnSe onGaAs +0.24 ZnTe on GaSb +0.08 ZnS/GaP −0.57 ZnTe on InAs +0.70 AlAs/GaAs+0.13 GaP/Si +0.37

As one can see in some of the cases (e.g. ZnSe/GaAs, ZnTe/GaSb, etc.)the V-group atom will not be replaced by a V-group atom but by aVI-group atom (Se, Te, etc.). This means that the replacement of atomsshall be considered as flexible as more factors such as, e.g. the ionicradius or other technological limitations are taken into account whenchoosing the replacement options. This also means that it is possible tochoose for pre-growth treatment of the substrate a chemical that it isnot a native precursor for either the substrate or the layer material.

From Table 2 one may also see that all other given examples by providemuch smaller (less than 1%) lattice mismatches, which are more favorablethan GaP/GaAs, and which give them a better chance for success. Inaddition, to make the “right” choice one should take into account alsowhat the desired application might be and some other related propertiesof the particular material candidate. For example, a brief comparison ofZnSe and ZnTe shows that ZnTe has about the same transmission range asZnSe but lower 2PA and 3 times higher nonlinear susceptibility at thedesired pumping wavelength of about 1 μm, i.e. ZnTe may be a betterchoice for nonlinear frequency conversion devices. Of course, one alsoshould pay attention to the specific technological limitations relatedto the growth of a particular material. For example, for the growth ofZnTe, according to the suggested chemistry, we shall use H₂Te for boththe pre-growth treatment of the substrate (GaSb) and the actual growthof ZnTe. However, the worldwide supply of H₂Te is relatively limited as,in addition, this gas is relatively unstable—even light assists in itsdecomposition—which means that the use of alternative Te precursors andchemistry paths is preferable. In contrast, H₂S is readily available anda well-known precursor, and the lattice mismatch of ZnS with the readilyavailable GaP substrates (and OP-GaP templates) is negligible (−0.569%).Regretfully, the nonlinear properties of ZnS are not as good as the NLOproperties of ZnTe, which does not mean that heteroepitaxially grown ZnS(large area ZnS substrates are also unavailable for homoepitaxy) cannotbe used for applications other than nonlinear frequency conversion.Another example of a technological limitation is that as of today GaPstill cannot be grown by HVPE directly on Si, but it can be grown athigh quality by MOCVD or MBE. From this point of view, although that thedisclosed method gives better chances for the growth of other materials(including some that have never been grown epitaxially in amonocrystalline shape, and in a size large enough for devicedevelopment) such as (ZnSe, ZnTe, ZnS, etc.), we continued to exploremore options. For example, PH₃ does not exhibit a strong effect on theSi surface during the pre-growth treatment, however, H₂Se dramaticallyattacks Si wafers with 4-degree miscut during the preheating stage (seeFIG. 24 ). Accordingly, the “third party” precursor (H₂Se) may be usedto pretreat the Si substrate with the idea to form a Si—Se transitionbuffer layer, which by introducing PH₃ in a later stage of pretreatmentor growth may gradually switch the process to the growth of GaP on theSi substrate. Such extended approaches of this disclosure will bepresented later in the text, but as one can see now, the options andvariations seem nearly unlimited.

With regard, again, to the GaP/Si growth (see Table 2) the poorer impactof some non-native precursors, and especially of PH₃, is probably due tothe strong Si—Si bond. In this case, bearing in mind that Si can handlehigher temperatures, instead of using an alternative precursor, theSi-substrates may be preheated only in H₂ to provoke some thermaldecomposition (as shown in FIG. 3B) to allow some Si-atoms to escape thesubstrate and thus, by releasing more atomic sites, to give a chance forthe approaching P-atoms released at the thermal decomposition of the PH₃molecules to occupy their positions. For the purpose, an additionaldetailed study of the thermal decomposition of Si wafers with differentorientations and miscut at different temperatures may be quite helpful.As an alternative, more studies for pre-growth etching of Si withdifferent Si dry or wet etchants may be necessary. The opposite growth,i.e. thick growth of Si on GaP is also possible. Moreover, in this casethe lattice mismatch is negative, which according to somecrystallographic considerations is even more favorable. In this case,the GaP substrate shall be pretreated in silane (SiH₄). Although GaP ismore expensive and with a lower quality than a Si substrate, it is moreimportant for the sake of further device development that a pureelectronic material (Si) is combined with a pure optical material (GaP),but it is not important which material is the substrate and which is thelayer material that will be growing on this substrate. Finally, althoughthe idea of this disclosure is, in general, to realize heteroepitaxialgrowths in cases where native substrates are unavailable or are of lowquality, the opposite growths of all the disclosed cases are a defaultpart of this disclosure every time when such opposite growths may favorone application or another.

All the new heteroepitaxial cases (see Table 2 and FIGS. 13A-13B) may beleveraged by their inclusion in related ternary or even quaternarymaterials that not only combine the best properties of two (or more)semiconductor materials (of course, in relation to the desiredparticular practical application), but that also facilitate theheteroepitaxial growth. In addition, the ternaries, in general, shallhave a closer lattice match to the parenting substrate materials thanthe parenting materials themselves, since the lattice constant of aternary shall always be between the lattice constants of the two parentmaterials. For example, the lattice constant of the GaAs_(x)P_(1-x)ternaries depending on the x-composition shall be between the latticeconstant of GaP (5,450 Å) and GaAs (5.653 Å). The lattice mismatch of aternary with any of the binary parent material substrate should besmaller than the lattice mismatch between the two parent materials.

Another direction that may be taken in developing this idea is to makethe lattice constants between substrate and growing layer closer bydoping the growing layer, while keeping in mind that doping with dopantsthat are different in size (i.e. smaller or larger ionic radius) willchange more or less the lattice constant of the doped material. On theother hand, the dopant concentration may be gradually changed duringgrowth, which will form a transition layer with a gradually changinglattice constant. This approach may secure an even smoother transitionbetween the substrate and the growing layer. Finally, the suggestedin-situ doping procedure conducted during the pre-growth treatment orduring the initial stages of growth may be replaced by some prior growthdoping procedure such as, for example, ion implantation. Indeed, ionimplantation is known as being capable of changing the properties,including the lattice constant, of a thin area of the target (in ourcase, the substrate) near its top surface. Each of these variations ofthe proposed substrate pre-growth pretreatment shall be followed bygrowth that aims to deposit a thin or thick epitaxial layer.

The following examples illustrate particular properties and advantagesof some of the embodiments of the present invention. Furthermore, theseare examples of reduction to practice of the present invention andconfirmation that the principles described in the present invention aretherefore valid but should not be construed as in any way limiting thescope of the invention.

EXPERIMENTAL

As illustrated in FIGS. 10A-10L, the related experiments were conductedin a hot wall 3-inch diameter horizontal quartz reactor 10 positioned ina three-zone resistive furnace 12. The furnace 12 is not depicted inFIGS. 10B-10L for clarity. If no ternaries are to be formed, the gasseslabelled as “ternary-forming gas” in FIGS. 10A-10L correspond to the“second precursor gas” of the claims. Mixtures of the second precursorgasses, in constant ratios or ratios varying over time, may be used tosupport the growth of ternaries, which may in turn support the growth ofthe desired growing layer. The sole “precursor gas” of FIGS. 10A-10Lcorresponds to the “first precursor gas” of the claims. The firstprecursor gas is usually hydrogen chloride (HCl) diluted to the desiredextent by the carrier gas (usually H₂). The role of the first precursorgas is to pick-up a II or III-group element (Al, Ga, In, Zn, Cd, Hg,etc.) from an open boat or a bubbler, and with it to form ametal-chlorine compound which is delivered to the mixing zone, making itavailable to participate in the growing process

The second precursor, or ternary-forming gas, is usually a hydride of aV or VI group element (AsH₃, PH₃, H₂Se, H₂S, SbH₃, etc.) diluted to thedesired extent by the carrier gas (usually H₂). The second precursor(ternary-forming gas), which is actually the precursor of the V or VIgroup element, is delivered to the mixing zone, making it available toparticipate in the growing process. We call the second precursor“ternary-forming” because the reactions between the first precursor gasand the ternary-forming gas on the foreign substrate may result in theformation of ternary islands on the substrate, which may eventuallycoalescence to form a continuous ternary transition buffer layer.

Example 1—Growth of GaP on GaAs Substrates, GaAs on GaP Substrates andGaAs_(x)P_(1-x) on Either GaAs and GaP Substrates, or all of them on theRelated OP Templates

These embodiments of the invention are based on the hydride vapor phaseepitaxy (HVPE) process, which results in thick heteroepitaxial growth ofGaP on GaAs substrates (or of OP-GaP on OP-GaAs templates)(see FIG.10A), or the opposite case of the heteroepitaxial growth of GaAs on GaPsubstrates (or on OP-GaP templates) (see FIG. 10B). However, one shouldbear in mind that even though these are two successfully realizedexamples, they are not the most favorable ones in terms of matchingtheir crystal lattices or matching their thermal expansion coefficientsor thermal conductivities. As explained in the text above, many othercouples of other semiconductor materials may be favored by the proposedapproach, i.e. grown by the proposed technique. The initial reason toinvolve GaAs substrates and OP-GaAs templates first was that they werereadily available at a relatively high quality and a reasonable price.In contrast, the quality of the available GaP substrates offered on themarket (and from here the quality of the fabricated OP-GaP templates)was much lower, which lowered the quality of the thick HVPE growth onthem. Their price was 5-6 times higher than the price of the GaAssubstrates. To choose to grow first GaP/GaAs but not the oppositeGaAs/GaP came also from the sign of the negative lattice mismatch. Thismeans that the GaP layer grows under tensile stress, which is the morefavorable case because this arrangement compensates the naturallycompressed surface of the GaAs substrate.

With regard to FIG. 10A, a quartz boat 14 positioned in the first zone16 and filled with molten gallium (Ga) was placed in a one-inch diameterinner tube 18 and a mixture of hydrogen H₂ as carrier gas and HCl as afirst precursor gas was flowed over the boat 14. The purpose of the H₂carrier gas is not only to carry the HCl precursor gas but also todilute the HCl flow to a desired extent while the HCl flow picks up somegallium (Ga) from the boat 14 to form gallium chloride, for examplegallium tri-chloride (GaCl₃) in the reaction:6HCl+2Ga→2GaCl₃+3H₂  (eq. 3a)However, forming gallium mono-chloride (GaCl) or gallium dichloride(GaCl₂) when HCl pass over the molten Ga is also possible in similarreactions as shown in the following equations 3b and 3c):2HCl+2Ga→2GaCl+H₂  (eq. 3b)2HCl+Ga→GaCl₂+H₂  (eq. 3c)Another peripheral flow, a mixture of hydrogen and phosphine (PH₃), as asecond precursor gas, in the case of GaP growth, or a mixture ofhydrogen and arsine (AsH₃) in the case of GaAs growth, or their mixture(PH₃+AsH₃) is mixed, again, with H₂ as a carrier gas and a diluter, inthe case of GaAs_(x)P_(1-x) growth, is introduced in the reactor 10 tomix with the GaCl₃ in the second reactor zone 20, called “mixing zone”,with the intention the gases in the mixture to react in such a way thatto form on the surface of the substrate 22, respectively, GaP, GaAs, ora GaAs_(x)P_(1-x) ternary layer. The same basic hardware is used in allvariations of the disclosed method depicted in FIGS. 10A-10L. While FIG.10A illustrates the growth of GaP or GaAs_(x)P_(1-x) on a GaAssubstrate, FIG. 10B illustrates the similar process of the growth ofGaAs or GaAs_(x)P_(1-x) on a GaP substrate. In this case the secondprecursor gas (or the ternary gas) is AsH₃ instead of PH₃ or it may betheir mixture PH₃+AsH₃ (all mixed/diluted with H₂). In this case, growthof the ternary on a GaP substrate, however, the content of phosphine inthe PH₃+AsH₃ mixture should be higher. This is intended to form aternary with a higher phosphorus content, which should have a smallerlattice mismatch with the GaP substrate, in contrast with the first casewhen an arsine rich PH₃+AsH₃ mixture shall form an arsenic rich ternarywith a lattice constant that is closer to the lattice constant of theGaAs substrate. The GaAs/GaP growth is considered as less favorable. Thereasons for that are: First, the material quality of the commercial GaPwafers is lower and, as a result, the quality of the fabricated OP-GaPtemplates is lower. This naturally leads to poorer thick HVPE growth onsuch lower surface quality surfaces. Second, the sign of the latticemismatch in the case of GaAs/GaP is positive, which means that, incontrast to the previous case (GaP/GaAs), the GaAs layer grows undercompressive strain that, according to some considerations is lessfavorable than the growth under tensile strain (GaP/GaAs). One mayovercome the poor quality of the commercially-available GaP substratesby creating a high quality GaP layer (according to the method of FIG.10A, and growing GaAs on that GaP layer. This technique may be appliedfor each of the examples presented herein. After forming GaCl₃ (eq. 3a)the most probable chemical reactions related to forming GaP on GaAs orGaAs on GaP are:GaCl₃+PH₃→GaP+3HCl  (eq. 4a)GaCl₃+AsH₃→GaAs+3HCl  (eq. 4b)These reactions are based on the assumption that when HCl is passingover the molten Ga it forms gallium tri-chloride GaCl₃. However, as wasshown in eq. 3b and eq. 3c, forming gallium mono-chloride GaCl orgallium dichloride GaGl₂ is also probable. In such cases, the aboveequations shall be differently balanced, as is shown below in equations4c and 4d for the case of forming GaP and in equations 4e and 4f for thecase of forming GaAs:2GaCl+2PH₃→2GaP+2HCl+H₂  (eq. 4c)2GaCl₂₊₂PH₃→2GaP+4HCl+H₂  (eq. 4d)2GaCl+2AsH₃→2GaAs+2HCl+H₂  (eq. 4e)2GaCl₂₊₂AsH₃→2GaAs+4HCl+H₂  (eq. 4f)The schematic of the process and its chemistry during the growth of theGaAs_(x)P_(1-x) ternaries are shown in FIG. 10C.

As one can see all other heteroepitaxial cases discussed further in thetext—some of which are illustrated in the following examples—havedistinct but similar chemistry.

Some typical values for the inner flows of H₂ and HCl, and the outerflows of PH₃ and/or AsH₃ related to the HVPE growth of GaP, GaAs, and/orGaAs_(x)P_(1-x) are provided in Table 3 below, as an example. However,these numbers are strictly correlated to growths of GaAs, GaP, or theirternaries and to the particular configuration of the HVPE reactor shownin FIG. 10A, e.g. a hot wall horizontal reactor with a 3-inch indiameter quartz tube with length of approximately 48-72 inches typicallykept at lower than atmospheric pressure. In these particular cases, thetotal gas flow was less than 400 sccm (standard cubic centimeters perminute, which means the flow that should be expected at “standard”conditions such as atmospheric pressure and room temperature). However,other reactor configurations or processes that involve other materialsand precursors may need different flows and flow regimes. In all cases,however, the total gas flow in the close-to-equilibrium HVPE processwill be much less than the huge (many liters) flows of gases typicallyused in far-from-equilibrium processes, such as MOCVD or MBE. At suchfar-from-equilibrium conditions, the process relies on highsupersaturation that provides conditions for massive irreversiblenucleation everywhere on the substrate surface.

TABLE 3 Some typical values for the inner and outer flows (sccm) of H₂,HCl, PH₃, and AsH₃ during growths of GaP, GaAs, or their ternaries.Inner Flow Outer Flow H₂ HCl H₂ HCl AsH₃ PH₃ 65-75 30-35 100-110 30-5070-80 50-60

With respect to the rest of the growth parameters, all experiments wereconducted with parameters within the following ranges: pressure <10Torr, substrate temperatures 720-740° C. for the growth of GaP(respectively 680-700° C. for the growth of GaAs), and V/III ratios inthe range of 2-3. These ranges provided conditions for aclose-to-equilibrium process at relatively low supersaturation(typically between 0.5-1.0), which is the nature of the HVPE growth.

Growth experiments were conducted homoepitaxially (GaP/GaP andGaAs/GaAs) and heteroepitaxially (GaP/GaAs and GaAs/GaP) on plain“on-axis” (100) GaAs and GaP substrates and on the same (100) substratesbut misoriented with 4° towards (111)B. As it was already mentioned, thegrowths of the GaAs_(x)P_(1-x) ternary at different x ratios wereperformed on both GaP and GaAs substrates (FIG. 10C). Homo- andheteroepitaxial growths were performed on the related OP templates, aswell. For example, homoepitaxy of GaP on OP-GaP templates and of GaAs onOP-GaAs templates, heteroepitaxy of GaP on OP-GaAs templates and GaAs onOP-GaP templates; and, finally, GaAsP on OP-GaAs and OP-GaP templates.

An important step in this process, strongly correlated to thisinvention, is related to the way of protecting the substrate 22 (FIGS.10A-10L) from thermal decomposition before growth begins. Suchprotection is generally limited to protecting the substrate from thermaldecomposition as in FIG. 3B, but not necessarily from other, desired,influences of the non-native precursors as presented in FIGS. 3C, 3D,4A-4D, 6A, and 9B-9D. For this purpose when the reactor temperaturereaches about 350° C. the substrate must be kept in either an AsH₃atmosphere, in the case of a GaAs substrate, or in a PH₃ atmosphere, inthe case of a GaP substrate. In the case of heteroepitaxy, we have moreoptions, each of which need to be effective enough. These choicesinclude the protection of a GaAs substrate in a PH₃ atmosphere or, viceversa, protection of a GaP substrate in an AsH₃ atmosphere. As analternative, we may also protect the wafer (substrate) by maintaining itin a mixture of PH₃ and AsH₃ gases. In all these cases one should keepin mind that, typically, the precursor flows, as well the hydrideprecursors, e.g. PH₃, AsH₃, H₂Se, H₂Te, SbH₃, etc., are diluted by thecarrier gas (H₂); as a practical matter, we use mixtures of AsH₃:H₂, orPH₃:H₂, or AsH₃:PH₃:H₂. One should also bear in mind that the growth ofother materials (see FIGS. 10D-10L) will require distinct chemistriesfor substrate-pretreatment and growth. For example, the growth of ZnSeon GaAs substrates (or OP-GaAs templates) requires pretreatment of theGaAs substrate (or OP-GaAs template) in an H₂Se:H₂ or an AsH₃:H₂Se:H₂precursor mixture. To fully explore the capabilities of the pre-growthstage, we conducted the preheating procedures not only in differentprecursor (or mixtures of precursors) atmospheres (flows) but also usingdifferent flow rates, different precursor ratios in the mixtures anddifferent gas regimes of introducing those gases following preliminarydetermined schemes. Further experiments of this nature were continued asthe preheating stage was followed by the stage of the epitaxial growth.The later experiments were performed in order to assess the impact ofthe initial stages of growth on the final layer quality. Finally, duringthe cooling stage the grown layers or OP structures had to be similarlyprotected from thermal decomposition keeping them in the relatedprecursor's atmosphere until the substrate temperature achieved the safelevel of about 350° C. or lower. The growths discussed in Example 1 arepresented schematically in FIGS. 10A, 10B and 10C.

Example 2—Growth of ZnSe on GaAs Substrates and OP-GaAs Template, asWell as the Opposite Growth of GaAs on ZnSe Substrates

This embodiment of the invention is based on hydride vapor phase epitaxy(HVPE) and the heteroepitaxial growth of ZnSe on GaAs substrates (FIG.10D) and OP-GaAs templates, and the opposite case of heteroepitaxialgrowth of GaAs on ZnSe substrates (FIG. 10E). Homoepitaxial growths ofGaAs on GaAs substrates and ZnSe on ZnSe substrates were also conductedin order to optimize the growth conditions. As explained in the textabove, many other semiconductor materials may be grown by this techniqueand are favored by the proposed approach. In the first case of thisexample—ZnSe/GaAs growth—the quartz boat 14 that is positioned in thefirst zone 16 of the furnace was filled with molten zinc. As a variationof this technique, the boat may instead of being filled with Zn may befilled with zinc chloride (ZnCl₂), or with a Zn-rich ZnCl₂-solution. Theboat was placed in a one-inch diameter inner tube 18 and a mixture ofhydrogen H₂ and HCl (first precursor) was flowed over the boat 14. Asexplained above, the purpose of the H₂ is not only to carry the HCl butalso to dilute the HCl flow to a desired extent while the HCl flow picksup some zinc (Zn) from the boat 14 to form zinc chloride (ZnCl₂). In thecase of using ZnCl₂, H₂ may be used simply as a carrier gas to deliverZnCl₂ to the mixing zone. Another peripheral flow, a hydrogen+hydrogenselenide (H₂:H₂Se) mixture is introduced as a second precursor in thereactor 10 to mix with the ZnCl₂ in the second reactor zone 20 (the“mixing zone”). The intention is to have the II and VI group (Zn and Se)species in the mixture react and to form a ZnSe monocrystalline layer onthe surface of the substrate 22. With regard to FIG. 10D, the process issimilar to that presented with regard to FIG. 10A, except that H₂Se isthe ternary-forming gas, and a layer of ZnSe is formed on a GaAssubstrate. This GaAs substrate, as a first step during the preheatingstage is, similarly, exposed to the non-native precursor, H₂Se, or tothe AsH₃:H₂Se mixture, in order to introduce Se atoms to start replacingAs atoms in the GaAs substrate and, eventually, form an intermediateternary GaAsSe transition layer. As a result, later during the initialstages of growth, possibly, this layer will convert gradually in aquaternary (GaAsZnSe) transition buffer layer, which also gradually willconvert growing in a pure ZnSe layer. In this case (FIG. 10D), indifference to the first three presented cases (FIG. 10A-FIG. 10C) thereplacement of the V-group atoms (As) in the substrate is not withV-group but with VI-group atoms (Se). Thus, as a result, the formedinitial ternary layer (GaAsSe) is not a combination from the twoparenting materials, i.e. the substrate and the layer.

Growth of ZnSe on GaAs substrates and on OP-GaAs templates is areasonable option for the growth of ZnSe because large area (enoughlarge for device development) ZnSe monocrystalline substrates are notcommercially available—the largest available “monocrystalline” ZnSesamples on the market are typically 5 mm×5 mm, and which still consistof several domains with different orientations. Consequently, OP-ZnSetemplates are unavailable, as well.

Heteroepitaxy of ZnSe on GaAs is also reasonable due to the very smalllattice mismatch (+0.238%) between ZnSe and GaAs. Fortunately, theavailability of high quality GaAs substrates, their reasonable price,and the maturity of two OP-GaAs template preparation techniques (thewafer bonding and the MBE assisted polarity inversion technique) providegreat opportunities for the growth of high quality crystalline ZnSe onnon-native GaAs substrates, as well as OP-GaSe on the high qualityOP-GaAs templates.

The advantage of ZnSe over GaAs and GaP is its wide and smooth IRtransparency and its smaller refractive index (see FIG. 26 ) which, ifthe pursued application is for frequency conversion devices, allowswider domains of the OP templates. This significantly facilitatessubsequent thick HVPE growth because it is easier to achieve good domainfidelity during the HVPE growth when the domains are wider.

Gas flow parameters for the growth of ZnSe on GaAs are similar to thosepresented in example 1. As depicted in FIG. 10D, the formation of ZnSeon GaAs (described below) is likely according to the reaction:Zn+2HCl→ZnCl₂+H₂  (eq. 5a)ZnCl₂+H₂Se→ZnSe+2HCl  (eq. 5b)(Note: We assume that when HCl pass over the molten Zn the formed zincchloride is zinc dichloride (ZnCl₂). However, mono (ZnCl) ortri-chloride (ZnCl₃) may be formed; the chemical equations must beproperly balanced, similar to the cases of gallium chloride discussedabove (eq. 4c-4f).)

The opposite case of heteroepitaxy of GaAs on ZnSe substrates is lessattractive for the same reasons and mostly because of the marketunavailability of large-area, good quality monocrystalline ZnSesubstrates, and the much higher prices of the small dimension ZnSesamples that are available. However, large area polycrystalline ZnSesubstrates are available and growth on them for other purposes stillmight be useful. Growths of GaAs on small monocrystalline ZnSesubstrates may be useful for some other applications, bringing theadvantage that in the case of GaAs/ZnSe the lattice match is the samebut negative, i.e. the GaAs layer will be tensely strained, whichaccording some considerations is more favorable.

As illustrated in FIG. 10E, the related opposite experiments for thegrowth of GaAs on ZnSe were conducted again in the same hot wall 3-inchdiameter horizontal quartz reactor 10 positioned in a three-zoneresistive furnace 12. A quartz boat 14 positioned in the first zone 16and filled with molten gallium (Ga) was placed in a one-inch diameterinner tube 18 and overflowed with a mixture of hydrogen H₂ as a carriergas and HCl (first precursor). Similar to the cases discussed in Example1, after forming the gallium chloride (GaCl₃) this inner flow was mixedin the mixing zone with the peripheral ternary gas flow, which was amixture between hydrogen (H₂) and arsine (AsH₃) with the idea to formGaAs on the surface of the ZnSe substrate. The chemistry was the same asduring the growth of GaAs on other substrates (see Example 1 and FIG.10B), for example, on GaP and in equations 4b, 4e, and 4f. A distinctionis that to start forming a ternary transition buffer layer on thesubstrate, the ZnSe substrate may be exposed to the non-nativeprecursor, which in this case is AsH₃ or a mixture the non-nativeprecursor and the native precursor, i.e. AsH₃+H₂Se, in both casesdiluted to the optimal extent with Hz. The temperature of the substratemay be slightly different as well, e.g. 800° C.-850° C., taking intoaccount the different properties of the various substrate materials—GaPin Example 1 and ZnSe in this Example 2. Optimal dilution depends of thematerial. For example, if the material is more volatile, e.g. P, itsprecursor (PH₃) should be less diluted than the least volatile, e.g. As,and the As precursor (AsH₃) should be more diluted. A rough estimationis that the diluted gas may be between 10-90% in the precursor flow.

The growths discussed in Example 2 are presented schematically in FIGS.10D and 10E.

Example 3—Growth of a Cubic Phase Zinc Blende Gallium Selenide Ga₂Se₃ onGaP and GaAs Substrates (and the Related OP-GaP and OP-GaAs Templates)and Hexagonal ε-GaSe on GaN (or AlN) Substrates (and the Related OP-GaNTemplates)

This embodiment of the invention is based on hydride vapor phase epitaxy(HVPE) and the heteroepitaxial growth of cubic phase zinc blende galliumselenide (GazSe₃) on GaP and GaAs substrates (FIG. 10F and FIG. 10G) andhexagonal ε-GaSe on GaN (or AlN) substrate (FIG. 10H) (and on therelated OP-GaP, OP-GaAs and OP-GaN templates), or the opposite cases ofthe heteroepitaxial growth of GaP and GaAs on a GazSe₃ substrates, andGaN or AlN on a hexagonal ε-GaSe substrate (the latter is not shownschematically in figures). Homoepitaxial HVPE growths of GaSe on GaSesubstrates were also conducted as a reference to the heteroepitaxialgrowth.

From point of view of transparency range, GaSe is as good as ZnSe butwith nearly 3-times higher nonlinear susceptibility (at λ=1 μm), makingit close to one of the leading materials for frequency conversiondevices, GaAs. At the same time using molten Ga instead, the fastevaporating Zn allows runs with longer durations, i.e. eventuallygrowing thicker layers with larger optical apertures. Regretfully,monocrystalline GaSe substrates larger than 10 mm×10 mm are unavailable,and even if they were available, GaSe is too soft (as soft as gypsumwith hardness only of 2 by Mohs) to be able to handle the heavy bonding,polishing, and etching procedures performed in the fabrication of OPtemplates. Fortunately, GaSe has several different crystallographicphases, two of which, a cubic phase zinc blende gallium selenide GazSe₃and hexagonal ε-phase GaSe have relatively close lattice matches (FIG.13 ) with three substrate materials, all of which are available in bothlarge area monocrystalline substrates and OP templates. This makes itpossible to attempt layer growths by using the method proposed in thisdisclosure, more specifically of a cubic phase zinc blende galliumselenide Ga₂Se₃ on GaP (FIG. 10F) and on GaAs (FIG. 10G), and ε-GaSe onGaN (or AlN) substrates and, eventually, on the related OP templates,OP-GaP, OP-GaAs and OP-GaN. Although the opposite growths of thesesubstrate materials should be, in general, possible on GaSe substrates,since such substrates are not available in sizes large enough for devicedevelopment or even for fabrication of OP-GaSe templates, we find suchgrowths as less reasonable and that is why they are not included in theprovided examples. However, the chemistry of such growths would,eventually, the same as in any other provided examples associated withthe growth of phosphides (GaP), arsenides (GaAs) or nitrides (GaN).

As illustrated in FIGS. 10F-10H, the related experiments were conductedin the same hot wall 3-inch diameter horizontal quartz reactor 10positioned in a three-zone resistive furnace 12. A quartz boat 14positioned in the first zone 16 and filled with molten gallium (Ga) wasplaced in a one-inch diameter inner tube 18 overflowed with a mixture ofhydrogen H₂ as carrier gas and HCl (first precursor). The purpose ofusing H₂ is not only to carry the HCl but also to dilute the HCl flow toa desired extent, e.g. 30-40%, with H₂ being 60-70% of the total H₂/HClmixture, while the HCl flow picks up some gallium (Ga) from the boat 14to form gallium chloride in one of the following compositions: GaCl,GaCl₂ or GaCl₃. Another peripheral flow, a mixture of hydrogen andhydrogen selenide (H₂Se) (second precursor), is introduced in thereactor 10 to mix with the gallium chloride in the second reactor zone20, the “mixing zone”, in order that the species within the mixturereact with each other and in surface reactions to form a GaSe layer onthe surface of the substrate 22. One of the probable chemical reactionsrelated to forming GaSe is:2GaCl₃+2H₂Se→2GaSe+4HCl+Cl₂  (eq. 6a)However, forming GaCl or GaCl₂ instead GaCl₃ or as fractions of thetotal gallium chloride flow is not excluded and in such cases eq. 6ashall be differently balanced as is shown below:2GaCl+2H₂Se→2GaSe+2HCl+H₂  (eq. 6b)GaCl₂+H₂Se→GaSe+2HCl  (eq. 6c)In these three chemical equations, however, the assumption is that theformed gallium selenide is the hexagonal ε-phase GaSe. For completeness,if we assume that the formed gallium selenide is the cubic phase zincblende Ga₂Se₃, for completeness equations 6a-6c shall be re-writtenafter replacing GaSe with Ga₂Se₃, as it follows:2GaCl₃+3H₂Se→Ga₂Se₃+6HCl  (eq. 6d)2GaCl+3H₂Se→Ga₂Se₃+2HCl+2H₂  (eq. 6e)GaCl₂+H₂Se→GaSe+4HCl+H₂  (eq. 6f)To be clear, while equations 6a-6c shall be used for the growth ofgallium selenide on the III-Nitride substrates (GaN or AlN), equations6d-6f shall be associated with the growths on GaP and GaAs substrates.It is worth also to mention that during all three growths the chemistryis the same because the same material, GaSe, is growing. However, sincethe substrates are different, the optimal growth temperatures for eachone of the substrates could be also different, but 500-900° C. or even720-850° C. is acceptable. Similarly, during the pre-growth treatmentall substrates shall be exposed to the same non-native precursor, H₂Se,with the expectation, however, that the composition of the intermediatebuffer layer will be different. Thus, the buffer layer on the GaPsubstrate shall be from GaPSe, while the buffer layers in the other twocases of growth on GaAs and GaN (or AlN) shall be, from GaAsSe and,respectively, from GaNSe (or AlNSe). Of course, exposing the substratesduring the pre-growth stage or some earlier stages of growth to amixture of the non-native and the native precursors (H₂Se+PH₃, orH₂Se+AsH₃, or H₂Se+NH₃) is always an option. As described above, allthese variations are related to either the growth of a cubic phase zincblende gallium selenide Ga₂Se₃ on zinc blende GaP or GaAs substrates, orhexagonal ε-phase GaSe (GaSe) on hexagonal substrates (GaN or AlN).Although from the point of view of lattice mismatch the most favorablecase was initially the growth of a cubic phase zinc blende galliumselenide Ga₂Se₃ on GaP (lattice mismatch of only −0.607%). As discussedin the results, the growth of a cubic phase zinc blende gallium selenideGa₂Se₃ on GaAs turned out to be most successful, even with the muchlarger lattice mismatch (−4.181%). The poor results of the GaSe/GaN isnot surprising, bearing in mind the large positive lattice mismatch(˜17%) between ε-GaSe and the III-Nitride substrates. However, the poorsurface morphology and crystalline quality obtained after homoepitaxy ofGaSe on a cubic phase zinc blende gallium selenide Ga₂Se₃ substrate isquite surprising. Obviously, all this leaves room for furtherimprovements related to this material.

In the opposite cases, which may be less reasonable, growths of thehexagonal wurtzite structure GaN or AlN shall be performed on thehexagonal ε-phase GaSe. One of the most probable chemical reactions forthe growth of GaN is:2Ga+6HCl→2GaCl₃+3H₂→GaCl₃+NH₃→GaN+3HCl  (eq. 7a),while for the growth of AlN, the most probable chemical reaction is:2Al+6HCl→2AlCl₃+3H₂→AlCl₃+NH₃→AlN+3HCl  (eq. 7b)Respectively, the growth of the cubic zinc blende GaP and GaAs shall beperformed on the cubic phase zinc blende gallium selenide (Ga₂Se₃) asthe most probable chemical reaction for the case of GaP growth is:2Ga+6HCl→2GaCl₃+3H₂→GaCl₃+PH₃→GaP+3HCl  (eq. 7c)while for the growth of GaAs the most probable chemical reaction is:2Ga+6HCl→2GaCl₃+3H₂→GaCl₃+AsH₃→GaAs+3HCl  (eq. 7d)Although equations 7a-7d are similar or the same as some of theequations given in Example 1 (e.g. eq. 3a, 4a, and 4b) they arepresented here again for more clarity. In general, the growth of thesame material follows similar chemical schemes no matter what kind ofsubstrate is used.

In three of the four growths described in Example 3, the growths of GaP,GaAs, and GaN need molten Ga as a source of the III-group elementprecursors. Only the growth of AlN needs molten aluminum as a source ofthe III-group element. From the examples provided in this Example 3 onecan also see that different materials (e.g. GaN, AlN, GaP) can be grownon different phases of the same material (cubic phase zinc blendegallium selenide Ga₂Se₃ and hexagonal phase gallium selenide ε-GaSe).This is another alternative variation of the proposed in this disclosuregrowth approach. In other cases, however, different materials may begrown on the same crystallographic phase of the same material but onsurfaces with different crystallographic orientations. This is possiblebecause the lattice mismatch in a particular direction may be smallerfor a particular material. Thus, it is known that the growth of cubicGaN is more favorable on (100) GaAs substrates, while the growth ofhexagonal GaN is more favorable on (111) GaAs substrates. This isanother alternative variation of the approach proposed in thisdisclosure.

Examples of heteroepitaxial growth of other selenides that are favoredby the proposed approach are, e.g. CdSe/InAs (lattice mismatch −0.139%)or even growths of other layered materials such as, e.g. InSe. In thelatter case the lattice mismatch and from here the substrate are notthat important as far as the most probable growth of a layered materialis through the van der Waals heteroepitaxy. Any substrate is acceptable.In these experiments, the II or III group material in the compound (inthis case Cd and In) determines the first precursor, which may be justmolten metal in the designated quartz boat 14. In contrast, the secondprecursor (the ternary gas) in all these cases may be hydrogen selenideH₂Se, which is also the non-native precursor for the pre-growthtreatment of these substrates. The chemistry in these two cases as alsopresented in the table in FIG. 13 is:Cd+2HCl→CdCl₂+H₂→CdCl₂+H₂Se→CdSe+2HCl  (eq. 8a)for the growth of CdSe, and:2In+6HCl→2InCl₃+3H₂→2InCl₃+2H₂Se→2InSe+4HCl+Cl₂  (eq. 8b)for the growth of InSe.(Note: The large variety of possible chemical paths shown in thisExample 3 is applicable to some extent in the rest of the given examplesbut for simplicity, they are not shown in such details. For the samereason the FIGS. 10A-10L, as well the examples in the table in FIG. 13 ,are provided only with one or two chemical equations corresponding tothe most likely reactions in each particular case.)

The growths given in this Example 3 are presented in FIGS. 10F-10H.

Example 4—Growth of ZnTe on GaSb and InAs Substrates

This embodiment (see FIG. 100 of the invention is based, again, onhydride vapor phase epitaxy (HVPE) and the heteroepitaxial growth ofZnTe on GaSb or InAs substrates. Such substrates are readily availableon the market at a reasonable price and relatively high crystallinequality for wafers with at least 2-inch diameter. In contrast, the ZnTesubstrates available on the market are either polycrystalline (at largersizes) or if they are “monocrystalline” they are relatively smallsamples which are not large enough for device development (e.g. forfabricating of OP templates) that, typically, still consist of severaldomains with different crystallographic orientations. That is why,although the opposite growths, i.e. the growths of GaSb or InAs on ZnTesubstrates are, in general, possible, we consider them as lessreasonable and for this reason we are not presenting them in detail inthis disclosure. However, large area, crystalline ZnTe substrates may begrown using the disclosed method. As illustrated in FIG. 10I, therelated experiments were conducted again in the same hot wall 3-inchdiameter horizontal quartz reactor 10 positioned in a three-zoneresistive furnace 12. The quartz boat 14 positioned in the first zone 16was filled with molten zinc (Zn) or with a Zn-rich solution of zincchloride (ZnCl₂). Proposing such alternative source of the II-groupelement is an attempt to solve the high vapor pressure of Zn, whichrestricts the duration of growth and thus limits the thickness of thegrowing ZnTe layer. The quartz boat filled with the II-group elementsource is, similar to the other growth experiments, placed in one-inchdiameter inner tube 18, and a mixture of hydrogen H₂ as carrier gas andHCl (the gas that will create the first precursor) is flowed over it.The purpose of the H₂ is, as described before, not only to carry the HClbut also to dilute the HCl flow to a desired extent, while the role ofthe HCl flow is to pick up some zinc (Zn) from the boat 14 to form zincchloride (ZnCl₂). As a recommendation, when Zn-rich ZnCl₂ solution isused instead of molten Zn, the H₂+HCl mixture shall be more diluted withH₂ since this alternative source of Zn already contains some ZnCl₂ andonly the excess of Zn in this saturated solution must react with theoverflowing HCl. Another peripheral growth, which is a mixture H₂+H₂Teis introduced into the reactor 10 to mix with the ZnCl₂ in the secondreactor zone 20, the “mixing zone”, in order for the species in themixture to react with each other and in surface reactions to form a ZnTelayer on the surface of the substrate 22. In both cases of growth oneither GaSb or InSe substrate, the second precursor (the ternary gas) isthe same, H₂Te. Since the growth is of the same material, ZnTe, nomatter the type of the substrate the chemistry of the process is alsothe same. One probable chemical reaction for forming ZnTe is:Zn+2HCl→ZnCl₂+H₂→ZnCl₂+H₂Te→ZnTe+2HCl  (eq. 9)The different substrate materials may require different temperatures forpre-growth treatment and growth, depending on the material properties.At the same time, although the substrates are pre-growth treated withthe same non-native precursor, H₂Te, the formed ternary transitionbuffer layer shall be different. Thus, in the case of a GaSb substrate,the treatment shall result in the formation of a GaSbTe ternary bufferlayer, while in the case of an InAs substrate the treatment shall resultin the formation of an InAsTe ternary transition buffer layer.

The advantage of growing ZnTe comes from the fact that ZnTe has thewidest and smoothest IR transparency among all known nonlinear opticalmaterials for frequency conversion, which starts conveniently in thevisible region and goes all the way down to 20 μm. At the same time, theZnTe nonlinear d-coefficient is almost as large as the d-coefficient ofGaAs. ZnTe, in addition, has one of the lowest two-photon absorption(FIG. 26 ).

However, there is one important inconvenience that one should take intoaccount when planning to use our approach for growth of ZnTe or othertellurides—the poor availability of H₂Te. As most of the hydrides,hydrogen telluride is corrosive, flammable, and poisonous. However, thereal reason for its very limited presence on the market is that H₂Te isan unstable gas, which decomposes easily; light facilitates thisprocess. To solve this issue, we propose instead of using H₂Te, toproduce it in-situ within the reactor volume as a part of the growthprocess. This approach, i.e. producing in-situ of a needed chemical,which is hard to provide or, which is a subject of serious hazardouslimitations, shall be considered as another variation of thisdisclosure, as far as we believe that it can be applied in other similarcomplicated cases.

H₂Te may be produced in-situ by using several commonly availableTe-precursors. The first idea was to use some of the metal-organictellurium precursors such as dimethyl or diethyl tellurium, which arealready used in the MOCVD growth of ZnTe. However, while thesemetal-organics are relatively expensive, their chemistry is relativelycomplex. The solution we propose in this disclosure is based on simplechemical compounds which are readily available at a reasonable price,which in this particular case are tellurium tetrachloride (TeCl₄),sodium telluride (Na₂Te), and N₂TeO₃. These chemicals, if not exactlyenvironmentally friendly, are at least not strongly poisonous. Ashydroscopic materials, we shall protect them from the environment ratherthan the environment from them. However, most importantly, they canrelatively easily produce H₂Te under rather ordinary conditions in onethe following simple chemical reactions:TeCl₄+3H₂→H₂Te+4HCl  (eq. 10a)Na₂Te+2HCl→2NaCl+H₂Te  (eq. 10b)2Na₂TeO₃+4HCl→4NaCl+2H₂Te+3O₂  (eq. 10c)(Note: In contrast to the other two chemicals, the price of Na₂Te isrelatively high. That is why we may choose to avoid the reaction shownin eq. 10b, although it is relatively simple.)

Some other heteroepitaxial growths of tellurides (not shownschematically but included as favorable cases in FIG. 13 ) includeGa₂Te₃/InP (or GaTe/InP), CdTe/InSb, HgTe/InSb, or HgTe/CdTe. Suchgrowths are also favored by the proposed approach by using chemistrysimilar to the growth of tellurides. In each of these additional cases,while the source of the II or III-group element is different—Ga, Cd, orHg metal—the source of the VI-group element (the ternary precursor gas)is always the same, H₂Te. The most probable chemical reactions forforming these compounds are:2Ga+6HCl→2GaCl₃+3H₂→2GaCl₃+3H₂Te→Ga₂Te₃+6HCl  (eq. 11)Cd+2HCl→CdCl₂+H₂→CdCl₂+H₂Te→CdTe+2HCl  (eq. 12)2Hg+6HCl→2HgCl₃+3H₂→2HgCl₃+2H₂Te→2HgTe+4HCl+Cl₂  (eq. 13)2Ga+6HCl→2GaCl₃+3H₂→2GaCl₃+2H₂Te→2GaTe+4HCl+Cl₂  (eq. 14)However, since the substrate materials are different for each of thesecases, each of them will have its own specific composition based on thematerial properties of the related substrate. Accordingly, thecomposition of the ternary or quaternary buffer layer formed as a resultof the pre-growth treatment in each individual case will be different aswell, but will be some combination of 3 or 4 of the elements, Ga, Te,In, P, As, and Sb. On the other hand, the decision as to how reasonablea particular heteroepitaxial growth is may be based on how “common”(i.e. how available and expensive) a given substrate is and howimportant from practical point of view the growing layer is. This is oneof the reasons why one might pay less attention to the opposite growths,including those related to the last four examples.

Some doped substrate materials may be a good solution for the growth ofZnTe substrates (and for other materials, as well). In general, manycommercially available substrate materials are undoped (orunintentionally doped), while others are n- or p-doped, even co-doped.The doping may occur during the growth of the crystal boule, when thedopant is distributed relatively uniformly in the entire volume of thematerial. However, the introduction of the dopant atoms may also be doneafter the boule is sliced into substrates by using techniques such asion implantation. In such cases the dopant atoms are introduced only toa small depth in the area near the substrate surface and do not presentin the entire substrate volume, which in some cases is enough. While themajor role of the doping is, in general, to change the materialproperties, it may also be used as another way of pretreating the sampleprior to growth. This, in another way, may facilitate the process ofheteroepitaxy from the point of view of ensuring a smoother transitionbetween the substrate and the growing layer and more efficient relief ofthe initial stress built at the growing interface due to the lattice andthermal mismatches. This is because the dopant atom, depending on itsionic radius, may change the lattice constant of the substrate material,making it closer to the lattice constant of the growing material. Forexample, GaSb substrates are offered on the market as undoped and dopedsubstrates, including some heavily doped with Zn. In this case theZn-rich GaSb:Zn substrates shall match closer to the growing ZnTe layerthan a regular undoped GaSb substrate. The degree to which the dopantatom will change the crystal cell of the substrate in the ‘right’direction and how much it will contribute to the formation of theternary transition layer shall be a subject of study in any particularcase. Doping or using properly doped (and eventually co-doped)substrates for the following heteroepitaxial growth is another variationof our approach presented in this disclosure.

Some of the cases presented in Example 4 are illustrated in FIG. 10I.

Example 5—Growth of ZnS on GaP and CdS on InP Substrates

This embodiment (see FIG. 10J) of the invention is based, again, onhydride vapor phase epitaxy (HVPE) and the heteroepitaxial growth of ZnSon GaP substrates and another sulfide, CdS, on another, InP, substrate.In these two separate cases both substrates, GaP and InP, arecommercially available with good crystalline quality and at reasonableprice for wafers with at least 2-inch diameter. In contrast, the ZnS andCdS substrates available on the market are either polycrystalline (atlarger sizes) or, if they are “monocrystalline”, they are relativelysmall samples not large enough for device development (e.g. forfabrication of OP templates), which typically still consist of severaldomains with different crystallographic orientations. That is whygrowths of ZnS/GaP and CdS/InP are reasonable, in contrast to theopposite growths, i.e. growths of GaP/ZnS or InP/CdS, although that suchgrowths are also possible due to the small lattice mismatches betweenthese two couples of materials. Whether heteroepitaxy or homoepitaxy ispreferred in a particular situation depends on numerous factors such asavailability, quality, and price of the related substrates andOP-templates, and the availability of the precursors needed to perform agiven growth, etc. Due to these factors, the properties of the grownmaterials with respect to the pursued applications and the close latticeand thermal mismatches, we believe that such growths are possible andreasonable. As illustrated in FIG. 10J, the related experiments wereconducted again in the same hot wall 3-inch diameter horizontal quartzreactor 10 positioned in a three-zone resistive furnace 12. The quartzboat 14 positioned in the first zone 16 was filled with molten zinc (Zn)in case of the growth of ZnS or with molten cadmium (Cd) in case of thegrowth of CdS. The as described quartz boat filled with the moltenII-group element (Zn or Cd), similarly to the other already describedgrowth experiments, is placed in one-inch diameter inner tube 18, Then amixture of hydrogen H₂ as carrier gas and HCl (the gas that will createthe first precursor) is flowed over the boat. The purpose of the H₂flow, as it was explained earlier, is not only to carry the HCl gas butalso to dilute the HCl flow to a desired extent. The role of the HClflow is to pick-up some zinc (Zn) in the case of ZnS growth or somecadmium (Cd) in the case of CdS growth from the boat 14 to form eitherzinc chloride (zinc dichloride ZnCl₂, or Zn mono-chloride (ZnCl), orzinc tri-chloride (ZnCl₃), or their mixture) in the first case (ZnSgrowth), or cadmium chloride (cadmium dichloride CdCl₂, or Cdmono-chloride (CdCl), or cadmium tri-chloride (CdCl₃), or their mixture)in the second case (CdS growth). Another peripheral growth, which is aH₂+H₂S mixture is introduced into the reactor 10 to mix with the ZnCl₂(or with CdCl₂) in the second reactor zone 20, the “mixing zone”, inorder for the species in the mixture to react with each other and insurface reactions to form a ZnS layer on the surface of the GaPsubstrate 22 or, respectively, to form CdS layer on the surface of theInP substrate 22. It is worth to mention that FIG. 10J illustratesgrowths of two different materials, ZnS and CdS, on two differentsubstrate materials, GaP and InP, using two different source of II-groupelement, molten Zn or molten Cd. However, since both growing materialsare sulfides, ZnS and CdS, the ternary precursor gas is one and thesame, H₂S. This does not mean that the ternary transition buffer layersare the same. On the contrary, due to the different substrates, theternary buffer layer after the pre-growth treatment of the substrate(GaP) with H₂S shall be from GaPS, while in the second case thepre-growth treatment of the substrate (InP) with H₂S shall be from InPS.The great advantage of using H₂S here, in comparison to the growths oftellurides (e.g. ZnTe), is that in the case of growth of sulfides theternary gas precursor, H₂S, is a well-known, readily availableprecursor. This allows skipping all steps (similar to those expressed byequations 10a-10c) that had to be taken to produce in-situ H₂Te duringthe growth of tellurides.

The most likely chemistry for growing ZnS and, respectively, CdS (andsome other sulfides), by the approach proposed here may be expressed bythe following chemical equations:Zn+2HCl→ZnCl₂+H₂→ZnCl₂+H₂S→ZnS+2HCl  (eq. 15a)and, respectively:Cd+2HCl→CdCl₂+H₂→CdCl₂+H₂S→CdS+2HCl  (eq. 15b)

In some cases, sulfides offer great advantages compared to othernonlinear optical materials. Let us compare, for example, ZnS with ZnTe.Next to the convenience of using one well-known, readily available, andrelatively cheap precursor (H₂S), ZnS, itself, offers several attractivefeatures, even compared in one direction only—as a nonlinear opticalmaterial for frequency conversion devices. The ZnS transparency does notgo very far into the infrared than that of ZnTe, but it starts atshorter wavelengths (see FIG. 26 ). Its nonlinear (d) coefficient atwavelengths of about 1 μm is visibly smaller than that of ZnTe, but itis still comparable to the d-coefficient of ZnSe (compare 20 pm·V⁻¹ vs.27 pm·V (see FIG. 26 ), as well to the nonlinearity of the birefringentlithium niobate (LiNiO₃). The highest nonlinear coefficient d₃₃ of thelater one (LiNbO₃) is 25 pm·V⁻¹, which corresponds with interactionsthat are parallel to the Z-axes, which direction is called 0-phasematching direction. Practically, in the direction of patterning, when wecall the material “periodically pulled lithium niobate”, or PPLN, theeffective nonlinear coefficient is even smaller—only 14 pm·V⁻¹. Not tomention that the nonlinear coefficient of ZnS is 1-2 orders of magnitudelarger that the d-coefficients of a number of traditional birefringentmaterials, e.g. potassium dihydrogen phosphate (KDP), whichd-coefficient is only 2.5 pm·V⁻¹, or ε-Barium borate (BBO) (2.5 pm·V⁻¹),or Lithium Triborate (LBO) (0.85 pm·V⁻¹). On the other hand, ZnS has oneof the lowest 2PA, about 2-2.1 cm/G⁻¹·W⁻¹ at the wavelength of interest(1.06 μm) (see FIG. 26 ). Actually, among all studied to date nonlinearoptical materials for frequency conversion devices, only GaP has lower2PA than ZnS (see FIG. 26 ). At the same time, ZnS has the smallestrefractive index n, only 2.36, among all of these materials. This,itself, allows the pattern of the OP templates to be with the widestdomains, which strongly facilitates the following thick HVPE growth oforientation-patterned ZnS. The line of advantages of ZnS, which hasnever been investigated thoroughly as a material for frequencyconversion (namely, because to date only polycrystalline ZnS iscommercially available) may be further extended, for example with thefavorable thermal properties of ZnS. Thus, the thermal conductivity ofZnS (see FIG. 26 ) is 27.2 W·m⁻¹·K⁻¹, which is significantly larger thanthe thermal conductivity of ZnSe, ZnTe, and GaSe, and comparable withthe thermal conductivity of the leading material in this field, GaAs. Inaddition, the thermal expansion coefficient is one of the smallest. Allthis makes ZnS a preferable candidate for such applications, if it couldbe grown in monocrystalline quality, most probably, onlyheteroepitaxially. According to all previous considerations, this ismade possible by the approaches provided in this disclosure.

Some of the cases presented in Example 5 are illustrated in FIG. 10J.

Example 6—Growth of Some Other Antimonides Such as GaSb and AlSb on InAsSubstrates, and AlSb Also on GaSb Substrates

As it was already discussed in Example 4 the opposite to the ZnTe/GaSbgrowth, i.e. the growth of GaSb on ZnTe is less reasonable due to thecommercial absence of large area monocrystalline ZnTe substrates.However, due to the small lattice mismatch of GaSb with InAs (+0.620%)and the availability of InAs substrates GaSb may be easily grown by thedisclosed technique on available InAs substrates, although GaSbsubstrates are available at about the same price and quality. However,there are a number of other reasons to prefer hetero-before homoepitaxy.An example is the case where the device development requires a structurecombining two or more materials with different bandgap energies. For thesame reason the more exotic material AlSb (relatively small latticemismatch of +1.273%) may also be grown on InAs substrates, although thelattice mismatch of AlSb with GaSb is smaller (+0.650%) and that is whythe growth of AlSb shall be more favorable on GaSb than on InAssubstrates.

This embodiment (see FIG. 10K) of the invention is based, again, on HVPEand the heteroepitaxial growth of GaSb and AlSb on InAs substrates andAlSb on GaSb substrates. As illustrated in FIG. 10K, the relatedexperiments were conducted again in the same hot wall 3-inch diameterhorizontal quartz reactor 10 positioned in a three-zone resistivefurnace 12. The quartz boat 14 positioned in the first zone 16 wasfilled with molten gallium (Ga) in case of the growth of GaSb or withmolten aluminum (Al) in case of the growth of AlSb. The quartz boatfilled with the molten III-group element (Ga or Al), similarly to theother growth experiments, is placed in one-inch diameter inner tube 18,Then a mixture of hydrogen H₂ as carrier gas and HCl (the gas that willcreate the first precursor) is flowed over the boat. The purpose of theH₂ flow, as it was explained earlier, is not only to carry the HCl gasbut also to dilute the HCl flow to a desired extent. Respectively, therole of the HCl flow is to pick up some Ga in the case of GaSb growth orsome Al in the case of AlSb growth from the boat 14 to form eithergallium chloride (gallium dichloride GaCl₂, or gallium mono-chloride(GaCl), or gallium tri-chloride (GaCl₃), or their mixture) in the firstcase (GaSb growth), or aluminum chloride (aluminum dichloride AlCl₂, oraluminum mono-chloride (AlCl), or aluminum tri-chloride (AlCl₃), ortheir mixture) in the second case (AlSb growth). Another peripheralgrowth, is when a H₂+SbH₃ mixture is introduced into the reactor 10 tomix with the GaCl₃ (or with AlCl₃) in the second reactor zone 20, the“mixing zone”, in order the species in the mixture to react with eachother and, hopefully, in surface reactions to form a GaSb layer or anAlSb layer on the surface of the InAs substrate 22 or, respectively, toform the AlSb layer on the surface of the GaSb substrate 22. The growthon the same substrate (InAs) in the first two cases (growth of GaSb orAlSb) does not mean that the ternary transition buffer layers are thesame because the source of the III-group element is different, Ga or Al.Thus, the ternary transition buffer layer in the first case is expectedto be from InGaAs, while in the second shall be from InAlAs. Similarly,although that in the second and the third case (growths of AlSb/InAs andAlSb/GaSb) we grow the same material (AlSb) using the same III-groupelement (Al), the ternary layers shall be again different because we areusing different substrate materials. Thus, when the substrate is InAsthe ternary transition layer shall be from InAlAs, while when thesubstrate is GaSb the ternary transition layer shall be from GaAlSb.Since in all these cases we are growing antimonides, the secondprecursor source, the ternary gas, should be SbH₃. The suggestedchemistry for these three cases are expressed by the following chemicalequations:2Ga+6HCl→2GaCl₃+3H₂→GaCl₃+SbH₃→GaSb+3HCl  (eq. 16a),for the case of the GaSb growth, and:2Al+6HCl→2AlCl₃+3H₂→AlCl₃+SbH₃→AlSb+3HCl  (eq. 16b),for the case of the AlSb growths.

Since AlSb is a material that is more exotic, and large areamonocrystalline AlSb substrates are unavailable, the opposite growth ofGaSb on AlSb is less reasonable (if not impossible at all), but theopposite growth of InAs on GaSb is as reasonable as the GaSb/InAsgrowth. Moreover, in this case the sign of the lattice mismatch isnegative, which means that the GaSb layer grows under tensile strain,which according to some studies is a more favorable case than thosegrown under compressive strain (positive lattice mismatch). In thiscase, the source of the III-group element is Ga, while the secondprecursor, the ternary gas, is SbH₃, which during the pre-growthtreatment of the InAs substrate shall form an intermediate InGaAsternary buffer layer. The probable chemical reaction for this growth is:2In+6HCl→2InCl₃+3H₂—InCl₃+AsH₃—InAs+3HCl  (eq. 16c)

Some of the cases presented in Example 6 are illustrated in FIG. 10K.

Example 7—Growth of AlAs on GaAs Substrates

The growth of AlAs on GaAs is an illustrative example of the usefulnessof the approach proposed in this disclosure. First, AlAs substrates arenot available, which comes with two conclusions. First, heteroepitaxy isthe only way to grow AlAs layers and, second, the opposite growth, i.e.GaAs/AlAs is unreasonable and, in general, impossible. The growth ofAlAs on GaAs is highly reasonable for the following reasons: First, therelatively small lattice mismatch (+0.127%) between AlAs and GaAs.Second, as a substrate material GaAs is almost as common as Si, i.e. itis widely available, with high quality and with relatively low cost.Third, OP-GaAs templates with high quality are readily available, whichmeans that growth of OP-AlAs may also be immediately attempted. Fourth,the band gap of AlAs is larger (different) than the bandgap of GaAs.Fifth, it is known that oxygen is the most common and least desirableimpurity in Al-containing semiconductor materials. By using metalaluminum, which has the highest possible purity (much higher than thepurity of any other Al-precursor) and by pre-making in-situ the firstprecursor (aluminum chloride) within the reactor chamber, the proposedapproach ensures the lowest possible oxygen levels in growing AlAs.

This embodiment (see FIG. 10L) of the invention is based, again, onhydride vapor phase epitaxy (HYPE) and the heteroepitaxial growth ofAlAs on GaAs substrates and, eventually, OP-AlAs on OP-GaAs templates.As illustrated in FIG. 10L, the related experiments were conducted againin the same hot wall 3-inch diameter horizontal quartz reactor 10positioned in a three-zone resistive furnace 12. The quartz boat 14positioned in the first zone 16 was filled with molten aluminum (Al) andplaced in one-inch diameter inner tube 18, Then a mixture of hydrogen H₂as carrier gas and HCl (the gas that will create the first precursor) isflowed over the boat. The purpose of the H₂ flow, as it was explainedearlier, is not only to carry the HCl gas but also to dilute the HClflow to a desired extent. Respectively, the role of the HCl flow is topick up some aluminum (Al) from the boat 14 to form aluminum chloride(aluminum dichloride AlCl₂, or aluminum mono-chloride (AlCl), oraluminum tri-chloride (AlCl₃), or their mixture). Another peripheralgrowth, which is a H₂+AsH₃ mixture is introduced into the reactor 10 tomix with the AlCl₃ in the second reactor zone 20, the “mixing zone”, inorder the species in the mixture to react with each other and in surfacereactions to form a AlAs layer on the surface of the GaAs substrate 22.In this case, the GaAs substrate is kept in the flow of its nativeprecursor AsH₃, which will protect the substrate from thermaldecomposition but will not initiate the formation of an intermediateAlGaAs transition buffer layer. This means that the pre-growth substratetreatment should be modified. For example, the growth may start with thedeposition of a low temperature buffer AlGaAs buffer layer. For thepurpose another source of molten Ga (in another quartz boat) should betemporary introduced in the reactor and positioned in the small one-inchdiameter inner tube 18 in order also to be flown by the HCL flow to formalso gallium chloride. This Ga source could be kept open even during theinitial stage of the growth but after that it should be removed orclosed. Another, technically easier option, is to supply the processwith Ga through another outside source as a bubbler with a gallium metalorganic precursor such as TMG (tri-metal gallium). This is anothervariation of our approach. The suggested chemistry of formation of theAlGaAs ternary buffer layer and the following HVPE growth of the AlAslayer on the GaAs substrate is expressed by the next equations:Al+Ga+6HCl→AlCl₃+GaCl₃+3H₂—AlCl₃+GaCl₃+AsH₃—Al_(x)G_(1-x)As+3HCl  (eq.17a)for the AlGaAs ternary layer formation, and:2Al+6HCl→2AlCl₃+3H₂—AlCl₃+AsH₃—AlAs+3HCl  (eq. 17b)for the HVPE growing AlAs layer.

Some of the cases presented in Example 7 are illustrated in FIG. 10L.

Example 8—Growth of Multilayered Structures

The disclosed method has another advantage—it may be used for the growthof multilayer structures in pursuing different applications. Forexample, growth may start on a GaAs substrate pretreated with PH₃followed by the growth of a GaP layer. In the next step, the grown GaPis pretreated with H₂S followed by the growth of ZnS taking advantagefrom the small negative lattice mismatches between GaP and ZnS (−0.57%).Thus we could have in one structure three layers (ZnS/GaP/GaAs) withincreasing bandgap energies (see FIG. 26 ) −1.42 eV (GaAs), 2.26 eV(GaP), and 3.54 eV (ZnS), which could find numerous practicalapplications. In this case, the reactor configuration should have morethan one inner tubes (in this case two) with more than one sources ofIII or II group elements (in this case a boat with molten Ga and a boatwith molten Zn). Respectively, there is a need for more than one (inthis case two) parallel lines for supplying more than one ternary gases(in this case PH₃ and H₂S).

Another example is the growth of a ZnSe/GaAs/GaP/Se multilayeredstructure. In this case, after the deposition of GaP on a Si substrate,the as grown GaP layer shall be pretreated in AsH₃. After the depositionof a GaAs layer on the GaP layer, as a next step the as grown GaAs layershall be pretreated in the flow of H₂Se after which to continue with theZnSe/GaAs growth.

These examples are only two of many other options for growth ofmultilayered structures for various practical applications. Growth ofmultilayered structures by using the approached provided in the text isanother variation of the disclosure proposed here. For simplicity, theexamples provided within the text of Example 8 are not illustrated onseparate figures.

Example 9: Growths after Prior Growth (In-Situ or Non-In-Situ) Treatmentof the Substrate with a Non-Native Material that is Also Non-Related tothe Substrate or the Layer Material Precursor

it was discovered that in some heteroepitaxial cases that the non-nativeprecursor typically associated with the growing material has less impacton the foreign substrate than another not related to the growingmaterial non-native precursor. For example, while PH₃ has almost noeffect on the surface of a Si wafer exposed prior to the intended directHYPE heteroepitaxy of GaP on Si, the exposure of a (100) Si wafer with4° miscut to H₂Se is visibly attacked by this non-native (to Si)material, which is also not related to the GaP layer precursor (see FIG.24 ). That is why, maybe, direct HVPE growth of GaP on Si was not verysuccessful. However, the Si substrate etched by H₂Se provides more sitesfor the approaching phosphorus or gallium atoms to adhere (realizing adirect GaP growth) or, if the Si-surface is saturated enough withSe-atoms, this may be used for the formation of an initial SiGaSe bufferlayer, which gradually may be converted into a GaSe buffer layer. Thiscould be a gentle prelude to the subsequent growth of GaP, which closelymatches the GaSe buffer layer GaP.

Si is, in general, inert to acids, except hydrofluoric acid (HF), whichis the aqueous solution of the gas H₂F. HF has the unique ability toreact with the naturally formed thin silicon oxide (SiO₂) layer (calledalso silica) when the material is even briefly exposed to air or water.HF forms with SiO₂ a hydrogen terminated layer of Si—H bonds in thereaction:SiO₂+4HF→SiF₄+2H₂O  (eq. 18)The hydrogen from this top surface layer may be used to form bonds withother chemical elements by treating the surface with other precursors,for example with H₂Se or PH₃. If the surface is, however, saturated withfluorine (F) atoms through the formation of SiF₄ (see eq. 18) such atreated Si-surface may be used for the growth of some fluorides, e.g.CaF₂ or BaF₂, which are also excellent optical materials. The pre-growthtreatment in this case may be done before introducing the Si substratein the reactor chamber in HF by following some standard or optimizedprocedures for treating Si in HF. The pre-growth treatment of the Sisubstrate may also be done in-situ within the reactor chamber byexposing the Si-wafer to HF gas flow. This option—pre-growth treatmentof the substrate in a suitable solution before introducing it into thereactor chamber is another variation of our approach along with theaforementioned “in-situ” pre-growth treatment of the substrate in anon-native related or not related to the layer material precursor.

The preliminary deposition of a thin buffer transition layer from thesame layer material by a different, typically, far-from-equilibriumgrowth technique, such as MOCVD or MBE, that was already described inthe text could be accepted as another alternative variation of a pre(HVPE) growth treatment of the substrate,

For simplicity, the examples provided within the text of Example 9 arenot illustrated in separate figures.

Example 10—Growths of Nonlinear Optical and Other Single or CompoundSemiconductor Materials on Halides

To this point the heteroepitaxy examples provided were related mostly toeither some well known As, P, or Sb-based semiconductor materials, e.g.GaAs, GaP, GaSb, etc., which may possess optical nonlinearity, orsimilar chalcogenide materials, i.e. materials containing S, Se, or Te,e.g. GaSe, ZnS, ZnTe, etc. However, there are still many other areas anddifferent kinds of materials to match where heteroepitaxy can be a greathelp. Such materials are, for instance, the halides, i.e. materials thatcontain F, Cl, Br, or I. Examples for using halides as substrates aretwo well-known optical materials with a broad range of transparency thatstarts in the ultraviolet (UV) range and continues all the way to themid- and long-wave IR (see FIG. 26 ), CaF₂, and BaF₂. These materials,by having inversion symmetry—a case when the first non-zero nonlinearoptical coefficient is the third order coefficient, do not provide theoption for frequency conversion by quasi-phase matching, which is asecond order nonlinear optical phenomenon. However, due to their closematch with some of the other nonlinear optical materials, they still maybe used as their non-native substrates. Moreover, having similarstructures, they still may be used for the fabrication of orientationpatterned templates, which may be facilitated by the fact that they aresofter materials (3 and 4 by Mohs scale) compared to 4.5 for GaAs and 5for GaP), which are more vulnerable to some etchants that will notdamage the grown material. For example GaP and GaAs may be grown onplain CaF₂ (negative lattice mismatches of −0.21% and +3.50%,respectively), or on the eventually fabricated OP-CaF₂ templates. Inthese two cases, the related (already explained in the text) substratepre-growth treatment procedures and chemistry paths for the growth ofphosphides and arsenides (see equations 4) shall be applied. Theopposite growth, i.e. growth of CaF₂ (traditional optical material) on acommon electronic material, Si (lattice mismatch of +0.57%) foroptoelectronic applications shall be also considered as favorable. Inthe case of BaF₂, there are also several good matching options such asAlSb (−0.98% lattice mismatch), GaSb (−1.61% lattice mismatch), InAs,CdSe, etc. In each of these individual cases, the nature of the pursuedapplication and which of the materials is more common (i.e. cheaper andmore available) shall be the criteria of which material should be thesubstrate and which should be the growing layer.

For simplicity, the examples provided within the text of Example 10 arenot illustrated in separate figures.

Example 11—Growths of Non-Ferroelectric Materials on FerroelectricSubstrates (GaP/LiNbO₃) and OP Templates (OP-LiNbO₃)

This example of the growth of a non-ferroelectric material (GaP) on asubstrate or an OP template from a ferroelectric material (LiNbO₃) is,at the same, time an example of the growth of a material with onecrystal symmetry (cubic) on another material with a different crystalsymmetry (trigonal). Furthermore, this is also an example for the growthof a traditional III-V semiconductor material (GaP) on a traditionaloxide material (LiNbO₃).

Although the in-plane (a-plane) lattice mismatch between GaP and LiNbO₃is relatively large (+5.87%), there are good reasons for choosing suchcombinations, among which is the extremely easy way for in-situpreparation of ferroelectric OP materials by growing them in aperiodically alternating electrical field. Such periodically polledLithium Niobate (PPLN) may be easily grown from melt by the conventionalCZ growth technique and eventually sliced into OP-LiNbO₃ templates. As afollowing step, thick HVPE growth of GaP is performed on these templatesusing the aforementioned chemistry for the growth of phosphides (seeequations 4). The unfavorable growth of GaP on the large matching LiNbO₃may be dramatically facilitated by the growth of either an intermediatetransition buffer layer or by a thin GaP layer on the LiNbO₃ substrates(respectively, the OP-LiNbO₃ templates). In the latter case, thedeposition shall be performed by a far-from-equilibrium growthtechnique, such as MOCVD or MBE. The reason for this is that thesetechniques have demonstrated in practice that, although they arefavorably less sensitive to the lattice mismatch, they can stilltransfer the polarity of the material underneath unchanged.

All of these examples of growth of one material on a substrate withdifferent crystal symmetries, or the growth of a non-ferroelectricmaterial on a ferroelectric substrate or template, or the growth of asemiconductor material on an oxide material, are variations of themethod disclosed herein. Another variation is the HVPE growth of a thicklayer on a thin layer (from the same or from a different material)deposited in advance on the substrate or on the template by a processthat is less sensitive to lattice mismatch, such as afar-from-equilibrium growth process, e.g. MOCVD or MBE.

For simplicity, the examples provided within the text of Example 11 arenot illustrated in separate figures. It should be also clear that byillustrating these examples with only one particular pair of materials,i.e. GaP and LiNbO₃, we do not put any limitations to other suitablematerials that may be suggested in each of the above particular cases.GaN, for example, is another material where the fabrication of OPtemplates is easy, due to the great deal of effort dedicated to polaritycontrol in III-Nitrides. This makes GaN and, in general, theIII-Nitrides candidates as substrates or templates for heteroepitaxy incases similar to these provided in example 11.

Some Basic Crystal Growth Considerations

Without being bound by theory, during heteroepitaxy the relation betweenthe forces that keep the atoms of the substrate in place and the atomsof the growing layer, Ψ_(AA) and Ψ_(BB) from one side and theinterfacial force Ψ_(AB) from the other side, is important. Thus, in thecase when Ψ_(AB)>>Ψ_(BB) and Ψ_(AB)≅Ψ_(AA) the interfacial force Ψ_(AB)is strong enough to produce pseudomorphous growth. As a result, duringpseudomorphous growth the lattice of the growing crystal B (e.g. GaP)will be, initially, homogeneously strained to fit to the lattice of thesubstrate crystal A (e.g. GaAs), which occurs at the expense of alinearly-increasing elastic strain. This, depending reciprocally on howlarge the lattice mismatch is, may typically continue to the depositionof no more than about 10-15 monoatomic layers. After this criticalthickness h_(c) (the thickness of the pseudomorphous growth), accordingto the misfit dislocation (MDs) concept, the pseudomorphous growth willbecome energetically unfavorable and the homogeneous strain will bereleased in the formation (in the ideal case) of MDs with a periodicityτ that should depend on the difference between the two lattice constantsa₀-b₀. (Note: Interfacial force, Ψ_(AB), is the force across theinterface between two faces that keep them together.)

The critical thickness h_(c) is, in general, larger when the latticemismatch in a particular heteroepitaxial case is smaller, i.e. fordifferent cases h_(c) increases with the decrease of the latticemismatch. However, the critical thickness does not depend linearly onthe linearly increasing elastic strain. Many other factors, such as thesign of the lattice mismatch, the mechanisms of MD formation or otheralternative mechanisms of strain relief, etc., must be considered inorder to predict this thickness. Most of these factors have beenincorporated into several models related to the particular case ofstress relaxation that occurs through misfit dislocation nucleation.Thus, taking into account the sign and the degree of the latticemismatch between GaP and GaAs (−3.57%) (See eq. 1) and the periodicityti of the MDs (˜28 interatomic distances) (see eq. 2), it was attempted,theoretically to determine the expected thickness of the pseudomorphousgrowth h_(c) in this particular case of GaP/GaAs growth (see FIG. 11 ).FIG. 11 illustrates the critical thickness h_(c) as a function of themisfit ƒ There, the upper dashed curve with the open squares is obtainedby energy minimization with a continuum model (the lower dashed curve)and is correlated to a negative (tensile) misfit. The solid curve withthe solid squares is obtained by minimization of the atomistic model forpositive (compressive) misfit. The two solid circles are the MDsimulation results for positive (compressive) misfit of ƒ=+2.5% andƒ=+5.0%, while the open circle is the simulation result for ƒ=−5.0%negative (tensile) misfit. (Note: that the error bar for the +5.0compressive misfit is smaller than the size of the solid circle symboland that is why does not appear in the figure.) The red dashed linesperpendicular to the ƒ-axis and h_(c)-axis in FIG. 11 show the case ofGaP/GaAs growth at a negative misfit of −3.57%. Thus, one can easily seethat at the negative misfit of −3.57%, when the GaP growstensile-strained on the GaAs substrate, the critical thickness must bein the range of 5-10 monoatomic layers after which theoretically the MDsshall start to appear with a periodicity τ (according to eq. 2) of about28 monoatomic distances. After such a rough estimation, we tried todetermine experimentally h_(c) and τ using high magnification TEM crosssectional images of areas near the interface between the GaAs substrateand the HVPE grown GaP layer (see FIG. 12 ) by looking for interruptionsin the regular lines of atoms parallel and perpendicular to theinterface.

When searching for the appearance of MDs, however, one should bear inmind that all theoretical works and simulations (such as thosegraphically expressed in FIG. 11 ) assume a flat interface and,typically, predict smaller critical thicknesses than those determined inexperimental studies. There is also a possibility, described in theliterature, that the strain that is due to the lattice mismatch may alsobe accommodated by 90° MDs that are parallel to the interface, renderingthem invisible on the provided cross sectional TEM images. In addition,in contrast to the relatively slow growth processes such as MOCVD orMBE, the faster HVPE growth may “seek” for faster alternative strainrelief mechanisms that may postpone or even entirely replace theformation of MDs. Such, as was determined in the case of GaP/GaAs (seeFIG. 12 ), are roughening of surfaces—having in mind the top layersurface or the interface—or formation of voids (which is actually theforming of new surfaces) above which, as it was once reported, thestrain is lower. Other types of compositional variations near theinterface, indicated by the contrast fluctuations shown by the arrows inFIG. 12D, are also possible. As for the case of growth of ZnSe on GaAssubstrates, as FIGS. 15A-15B indicate, the strain relaxation, again,proceeds through the formation of stacking faults, which originate fromthe GaAs substrate (FIGS. 15A-15B) rather than through the formation ofMDs. Another possibility is that the interfacial force Ψ_(AB) is justnot strong enough to produce pseudomorphous growth, or that the P atomsreplacing some of the As atoms in the GaAs crystal cell (forming GaAsP)diminish the need for a pseudomorphous growth. All this means that eachparticular heteroepitaxial case and each used growth approach may haveits own specificity in relieving the strain built in as a result oflattice and thermal mismatches between substrate and growing layer.

Characterizations

Each pretreated or grown sample was characterized with regard to itssurface morphology and crystalline and optical quality by at leastseveral of the following characterization techniques: cross section andtop layer surface Nomarski optical imaging, x-ray diffraction (XRD),scanning electron microscopy (SEM), atomic force microscopy (AFM),tunnel electron microscopy (TEM), electron dispersion spectroscopy(EDS), optical transmission, and linear and nonlinear opticalabsorption. Each of these material characterizations was performed inorder to reveal the mechanisms of the formation of defects near theinterface between the substrate and the growing layer, and also howthese defects propagate in the layer and how they impact the final layerquality, taking into account the impact of the applied pretreatmentconditions and the applied growth parameters during the growth stage.

Characterizations related to the surface morphology, the crystallinelayer quality, and other electrical and optical parameters related tosome specific practical applications were used also as a feedback to thegrowth process that allowed the determination of the optimal parametersfor pretreating and growth, e.g. substrate and mixing zone temperaturesand the rates of their increase or decrease, reactor pressure, V-IIIratios, gas flow regimes, etc., for a number of different materialcases.

From the dark field TEM images of GaP grown on GaAs sample (see FIG. 2B)it was confirmed that, as it was predicted (see FIG. 2A), the biaxialstrain 6 during growth of GaP/GaAs may be resolved into a uniaxial shearstress τ on the (111) dislocation glide plane. As a result, edge, screw,and mixed dislocations do appear along the (111) zone; as in the case ofa Burger vector G=002 both edge and mix dislocations are observed, whilein the case of G=002 screw and mix dislocations are observable (see FIG.2B). The good news is that after the first 1-2 μm of growth, which arehighly populated with dislocations, the dislocation density starts tonoticeably decrease with layer thickness. Thus, as our cross sectionlinear transmission measurements indicated, in the next couple ofhundreds of microns the material demonstrates good IR transparency,which is the first precondition for using these materials for frequencyconversion applications. Finally, the growing layer is terminated by asmooth top surface morphology with an average roughness RMS<1 nm for a 1μm² AFM scanning spot. Such a self-healing effect was noticed during theHVPE growth of many other materials too, for example, in the case ofHVPE grown GaN. This decrease of the dislocation density with theincrease of the layer thickness is usually associated with the increaseof the probability of two opposite treading dislocations that appear atthe interface to fall within their interaction cutoff, eventually,annihilating each other.

Our measurements indicate that we have determined good controlparameters for engineering the transition buffer layer, particularlywith regard to its thickness, composition, and quality, which allows asmooth transition between two mismatched materials.

For example, we demonstrated that by extending the idea of thetransition buffer layer to the growth of a thick ternary layer, we wereable to achieve hundreds of microns thick layer of GaAs_(x)P_(1-x) witha changing composition. In a particular series of experiments we grew300-700 μm thick GaAs_(x)P_(1-x) with compositions within the range ofx=0.1-0.91 as the growth on plain (GaAs) substrates (FIGS. 19A-19B),which were intended for linear and nonlinear optical measurements(linear absorption and transmission, 2PA and nonlinear susceptibility)(FIGS. 20A-20B), while the growths on orientation-patterned (OP-GaAs)templates (FIGS. 21A-21F) were dedicated to demonstrating ternaries infrequency conversion and device development. Examples of typical ternarycompositions are GaAs_(0.34)P_(0.66) and GaAs_(0.61)P_(0.39).GaAs_(x)P_(1-x) ternaries are attractive due to the possibility ofcombining in one material having the higher nonlinear susceptibility ofGaAs with the lower 2PA of GaP (FIGS. 20A-20B), meaning a material witha higher nonlinear susceptibility than GaP but a lower 2PA than GaAs.Shifting the edge of the strong 2PA from 1.7 μm (in GaAs) towards theshorter wavelengths (under 1.55 μm in GaAs_(x)P_(1-x)) is alsoattractive because it brings the advantage of using readily availablepump sources at 1.55 μm and under, which are currently used in thetelecommunication industry.

Another advantage of ternaries, and specifically of GaAsP, can be easilyseen on the phase-matching curves for GaAs (FIG. 22A) and GaP (FIG. 22B)plotted for 2 different pump wavelengths, 1.06 μm and 1.55 μm. Thus, toachieve the same output wavelength (see y-axis) one will need anOP-template which pattern has averagely 2-3 times wider domains (largercoherence length) (see x-axis) in the case of OP-GaP compared to thecase of OP-GaAs. This strongly facilitates the thick HVPE growth on thetemplate since maintaining good domain fidelity during the growth ismuch easier at wider domains. This tells us that a GaAsP ternary notonly will be able to be pumped at shorter wavelengths but will alsopossess a dispersion that will allow patterns with larger domain widths,which significantly facilitates the HVPE growth on the OP-template. Asimilar conclusion for the advantage of ZnSe vs GaAs can be easily madeif one compare the phase-matching curves of OP-ZnSe (FIG. 22C) andOP-GaAs (FIG. 22C). In addition, depending on the composition, ternariesmay be grown on either one of the parenting materials, e.g. GaAs or GaPfor a GaAsP ternary. For example, it is more suitable to growGaAs_(0.61)P_(0.39) on GaAs substrates or OP-GaAs templates, while thegrowth of is GaAs_(0.34)P_(0.66) is more reasonable on GaP substrates orOP-GaP templates. Some useful information related to the growth ofGaAs_(x)P_(1-x) is provided in FIG. 23 , which presents dependence ofthe growth rate on the ternary x-composition. According to FIG. 23 ,when the composition is closer to a binary material, e.g. GaAs or GaP,the growth rate is faster (with the trend for GaAs to grow, generally,faster than GaP) but slows down for compositions in the middle. Inaddition, ternaries are always more favorable heteroepitaxial cases dueto the smaller lattice mismatches with the parenting substratematerials. Thus, ternaries are a good solution for improvedheteroepitaxial growth at lower lattice mismatches, which directlyfavors the intended device developments. Giving GaAs_(x)P_(1-x) as anexample of ternaries is not intended to restrict other ternaries orquaternaries (included or not included in the texts of this disclosure),which may be based on other material combinations, or to take advantageof the ideas for their growth or practical use in the same or similar tothe described here applications.

By demonstrating that heteroepitaxy is possible and successful in someless favorable cases (e.g. GaP/GaAs and GaAs/GaP) we have opened thedoors wide for other heteroepitaxial cases (e.g. ZnSe/GaAs; ZnTe/GaSb;ZnTe/InAs; AlAs/GaAs; GaSe on GaP, GaAs, or GaN; ZnS/GaP; and evenGaP/Si) that often provide closer, more favorable lattice and thermalmatches. As provided in the Experimental results above, many of thesecases have already been successfully grown by our technique in largesize substrates (halves or quarters of 2-inch wafers) with high surfaceand crystalline quality. For example, up to 500 μm thick ZnSe withsmooth surface morphology and FWHM of about 60 arcsec of XRD 2theta-omega scan was grown with growth rate of up to 105 μm/h as it isshown in FIGS. 14-16 . In some of these cases, due to the high Zn-vaporpressure, which restricted the duration of growth to about 2 hours,achieving thicker layers demanded a re-growth, which was possiblewithout any need for polishing of the layer after the first growth. Thesuccessful growth of ZnSe/GaAs is another example of the power of theproposed heteroepitaxial approach because, to date, most of thecommercially available ZnSe substrates are polycrystalline, and if theyare crystalline, they are unpractically small, with poor crystallinequality, and very expensive.

In this series of experiments, cubic phase gallium selenide with zincblende symmetry (Ga₂Se₃) was grown on GaP (FIG. 17A) and GaAs (FIG. 18 )substrates, while hexagonal ε-phase gallium selenide (GaSe) wasattempted on GaN substrates (FIG. 17B). While the poor quality of thegrowth on GaN (FIG. 17B) can be explained by the large lattice mismatchbetween GaN and GaSe, the poor quality of the growth on GaP at such asmall lattice mismatch between GaP and GaSe (FIG. 17A) was surprising.For comparison the growth of gallium selenide was performed alsohomoepitaxially (FIG. 17C) on a monocrystalline hexagonal ε-GaSesubstrate, which surprisingly resulted not in a continuousmonocrystalline GaSe layer but in numerous differently sized anddifferently oriented ε-phase hexagonal GaSe flakes (FIG. 17C). The mostsuccessful growth was the growth of the cubic phase gallium selenidewith zinc blende symmetry (Ga₂Se₃) (FIG. 18A) on the GaAs substrate.Thus, for the first time low-dimensional Ga₂Se₃ was grown by HVPE in theshape of large area continuous monocrystalline layers with thicknessesin the range of 0.2-4.5 μm on GaAs substrates (FIGS. 18A and 18B). Anindication of their good quality was the EDS analysis (FIG. 18C) andalso the HR-XRD of these samples, which clearly revealed cubic phaseGa₄Se₆ (or just Ga₂Se₃) with zinc blende structure and excellent surfaceand crystalline quality (FIGS. 18D and 18E).

Although ε-GaSe has been used for a long time for phase matchingfrequency conversion in the mid-IR, GaSe, has never achieved theubiquity of other NLO materials in commercial and industrialapplications due to the difficulties associated with the growth processand sample preparation. This comes from the fact that GaSe has a layeredstructure with weak interlayer van der Waals bonding and, further,hardness close to zero by the Mohs' scale. The numerous phases in whichthis material can exist (even co-exist in a single sample) bringsadditional complexity to the growth process. In contrast to thehexagonal ε-phase GaSe (suitable for phase matching frequencyconversion) the cubic phase zinc blende Ga₂Se₃ could be an alternativematerial for quasi-phase matching frequency conversion. However,although Ga₂Se₃ has been grown as single crystals, large enoughcrystalline gallium selenide is not practically available, plus, such asoft material cannot handle the heavy polishing and etching proceduresassociated with the preparation of an OP-template. These two reasonsmake heteroepitaxy the only option for the growth of gallium selenidefor QPM frequency conversion. Fortunately, the zinc blende Ga₂Se₃ hasabout the same lattice mismatch with GaAs (−4.02%) as GaP with GaAs(−3.57%). This supports for favorability of Ga₂Se₃/GaAs heteroepitaxyand, eventually, the growth of OP-Ga₂Se₃ on OP-GaAs templates, similarto GaP/GaAs and OP-GaP/OP-GaAs heteroepitaxy. Realizing HVPE growth ofcontinuous layer zinc blende Ga₂Se₃ with smooth surface morphology andexcellent crystalline is a good opportunity to grow this excellent NLOmaterial for QPM frequency conversion in the MLWIR. However, the evencloser lattice mismatch with GaP (−0.42%) supports the heteroepitaxy ofGa₂Se₃/GaP. Moreover, other applications of that would findheteroepitaxy of the cubic zinc blende gallium selenide on the closelattice matched Si are also attractive. For example, in contrast to sometraditional 2D materials, wherein zero bandgap energies restrict themfrom their use in logic electronics or for field-effect transistors(FETs), the low-dimensional GaSe has the advantage that its bandgapenergy may be tuned by the number of the deposited monolayers, which areeasily controlled by growth duration. In addition, GaSe has a strongphoto-response, which makes this material suitable for photodetectors.The growths of GaSe presented herein are classic examples of van derWaals heteroepitaxy, which is another variation of the invention.

According to FIG. 1 and FIG. 13 , in addition to the cases alreadydiscussed, there are a number of other favorable heteroepitaxial casesthat are determinable by the lattice mismatch between the substrate andthe growing layer. Such cases include, for example, CdS/InP (−0.624%lattice mismatch), or vice-versa, i.e. InP/CdS (+0.624% latticemismatch), AlSb/GaSb (+0.650% lattice mismatch), CdSe/InAs (−0.139%lattice mismatch), GaSb/InAs (+0.620% lattice mismatch), AlSb/InAs(+1.273% lattice mismatch), CdTe/InSb (+0.040% lattice mismatch),InSb/CdTe (−0.040% lattice mismatch) or vice-versa CdTe/InSb, HgTe/CdTe(−0.447% lattice mismatch), HgTe/InSb (−0.407% lattice mismatch), oreven CdS/ZnS (+7.064% lattice mismatch) or vice-versa ZnS/CdS. Althoughin the latter case the lattice mismatch may be considered as large,there are a number of techniques and growth modes (explained above) thatmake heteroepitaxy possible. A great example of that is the growth ofGaN on sapphire, where the initial lattice mismatch is huge, −33.354%.The disclosed techniques may be successfully applied in another exampleof a relatively large lattice mismatch of +5.87%, when GaP is grown onperiodically poled LiNbO₃ (PPLN). This heteroepitaxial case of thegrowth of a semiconductor material with excellent nonlinear opticalproperties, GaP (FIG. 13 ) on an excellent optical oxide ferroelectricmaterial, LiNbO₃, is especially attractive, because the polarityinversion in ferroelectric materials is easy and does not require thepreparation of OP-templates. Growth of semiconductor materials onoptical materials or on ferroelectric materials are other variations.Growths of other semiconductor materials on other optical materials (butnot oxide materials) such as GaF₂ and BaF₂ are also attractive due tothe small lattice mismatches, especially in the cases of GaP/CaF₂,GaAs/CaF₂, or AlSb/BaF₂ and GaSb/BaF₂ (see FIG. 13 ). Growths ofsemiconductor materials on optical materials, which are neither oxidenor ferroelectric materials, is another useful variation.

From point of view of lattice mismatch, many of the heteroepitaxialcases presented in FIG. 13 are more favorable than the first realizedcase—GaP/GaAs (−3.574% lattice mismatch), which is a good preconditionfor their success. The concept was demonstrated successfully in thegrowth of ZnSe on GaAs (only +0.238% lattice mismatch), and the growthsof GaSe on different substrates, e.g. cubic phase zinc blende galliumselenide Ga₂Se₃ on GaAs (−4.02% lattice mismatch). The mixed resultswith the more favorable case of Ga₂Se₃/GaP (−0.42% lattice mismatch,only) is attributed to the diversity of GaSe phases, and the imperfectoptimization of the growth conditions, which also explains the imperfectquality of the GaSe/GaSe homoepitaxial growth.

In one of the example in FIG. 13 (InSe) a substrate material is notspecified. This is because there are some contradictions in theliterature in regards to the InSe crystal structure and latticeconstants. In addition, such as in the already proven case of GaSe/GaAsgrowth, InSe is a typical 2D material. Such materials may be grown onvarious substrates because in such cases the layers are held to thesubstrate by van der Waals forces, a case when the lattice mismatch doesnot play such an important role, as opposed to the other cases discussedabove. Thus, the disclosed approach gives one the opportunity to growheteroepitaxially numerous other 2D van der Waals semiconductormaterials, such as elemental 2D semiconductors, chalcogenides,phosphides, arsenides, iodides, and oxides. Thus, van der Waalsheteroepitaxy is another important alternative variation of thistechnique.

As taught above, however, the lattice mismatch is not the only importantcriterion when matching two materials in a growth process. First, to bepractical, the substrate material should be available in a relativelylarge size (e.g. at least 2-inch wafers), at a reasonable price, andwith high surface and crystalline quality; the so-called “epi-ready”surface. The availability of such substrates indicates a mature growthand wafer preparation technology, as well viable OP template preparationtechniques. Next to the well-known, common substrates, e.g. Si, Ge,GaAs, or GaP, some other materials, e.g. InAs, InP, InSb, GaSb, and CdTeare also available as substrates for subsequent epitaxial growth. Fromthis point of view, it makes perfect sense to grow materials that areeither more expensive or not available in a large size and goodcrystalline quality, e.g. ZnSe, ZnTe, or GaSe, on common or high qualitysubstrates, e.g. growth of crystalline ZnSe/GaAs, ZnTe/GaSb, orGaSe/GaAs, etc., as well on the related OP templates, when they areavailable. In the same way, it is much more reasonable to grow CdSe,which is also not available as large crystalline substrates, on InAs,which is available at high quality and at a reasonable price of about$100 per 2-inch wafer. Similarly, it is preferable to grow CdS (about$2,000 per 2″ wafer) on the cheaper InP (about $400 per 2-inch wafer)than to perform the opposite growth, i.e. InP/CdS. Also to be consideredare the growths of zinc-blende (cubic) materials on zinc-blende (cubic)substrates (e.g. GaP/GaAs), or wurtzite (hexagonal) materials onwurtzite (hexagonal) substrates (e.g. GaN/sapphire) rather than, forexample, a zinc-blende material, which has a cubic symmetry, on awurtzite substrate, which has a hexagonal symmetry. One also should bearin mind that different crystallographic orientations might provide acloser lattice match to different phases of one material. Thus hexagonalGaN may be successfully grown on (111) GaAs substrates, while cubic GaNmay be grown on (100) GaAs. The opposite arrangement, i.e. that twodifferent phases of the same material could be grown successfully oncompletely different materials is also possible in many particularcases. Thus, as described above, Ga₂Se₃ can be grown on GaP, whileε-GaSe can be grown on GaN (for more examples see FIG. 13 ). In order tosimplify the chemistry, it is also preferable to grow antimonides onantimonides, or selenides on selenides, etc., than, for example,antimonides on sulfides, even when this is at the expense of a largerlattice mismatch. Thus, for example, the case AlSb/GaSb should bepreferred to the case of CdSe/InAs. However, this as many otherrecommendations presented here, shall not be accepted as a strict rulebecause there are cases when growth of a layer on the same type ofsubstrate material may result in lower surface quality expressed by, forexample, a larger number of misfit and treading dislocations. Someexamples: 1) InAs/GaSb have much smaller lattice mismatch (−0.615%) thanInAs and GaAs (+7.165% lattice mismatch) and that is why it should bepreferred; 2) the CdSe/InAs growth should be also preferred due to thenegligible lattice mismatch of −0.139%, even though they arecombinations of semiconductors from different groups—II-VI and III-V.

Many other factors important to the growth process should also be takeninto account. For example, the lack of a H₂Te precursor on the marketand its easy decomposition to H₂ and Te (most probably before to havethe chance to react with the other chemicals involved in the growth)require a search for alternative chemical approaches in the growth oftellurides, for example, in the growth of ZnTe. One of these approachesis to produce in-situ H₂Te within the reactor volume using otherchemicals and chemical reactions, e.g. thermal decomposition of TeCl₄ inthe flow of H₂ or H₂+HCl mixture (see eq. 10a), or other options shownin eq. 10b and eq. 10c (see also FIG. 13 ).

Next to the already described compound semiconductor substrates we mayalso add some more details about using some traditional optical (CaP₂ orBaF₂) or ferroelectric (LiNbO₃) or non-ferroelectric materials assubstrates, including some perovskites (e.g. BaTiO₃), some of which werealready mentioned above and in FIG. 13 . The reason for that is not onlythat many of these new substrate materials can be found on the market ina reasonable size, quality, and price (e.g. $50-$100 per a 100 mmdiameter wafers), but also because they could have small lattice orthermal mismatches with the above mentioned semiconductor materials (seeFIG. 13 ). With this, we enter in territories where we shall growtogether not only the same structured materials, but also materials withdifferent natures, chemical compositions, structures, symmetries, andproperties, e.g. traditional optical or electronic compoundsemiconductor materials with traditional optical materials,ferroelectrics or perovskites, oxides, chalcogenides, fluorides,nitrides, etc. Fortunately, in many of these cases nature providesendless options, which we just must discover. In others, however, when asuitable self-organizing growth mechanism does not yet exist, moreresearch efforts are necessary in engineering the transition bufferlayer between the substrate and growing layer. One possible way for“fitting”, for example, fluorides with oxides structures is “byinterleaving isostructural components that are sharing structurallyidentical cation and anion sub-lattices”. A great example of a naturalself-organizing mechanism (already mentioned above) is the growth of GaNon sapphire with which GaN has the huge lattice mismatch of 33%.However, if the growth starts with nitridation of the surface (in anammonia rich atmosphere) this will initiate growth of AlN with which GaNhas a lattice mismatch of 2.5% only. From first sight, this “pre-growth”does not make any sense, because the lattice mismatch of AlN andsapphire is even larger (35%). Fortunately, during this initial growththe AlN lattice cell rotates 30 degree towards the sapphire latticecell, which minimize the system energy. This rotation reduces theAlN/sapphire lattice mismatch from 33% to 13.3% so now AlN can grow onsapphire, which allows in a later stage the growth of GaN on the initialAlN layer.

One should also bear in mind that, as described above, from acrystallographic point of view, growth at a negative mismatch thatresults in a tensile strained growing layer is more favorable thangrowth performed at a positive mismatch, i.e. under compressive strain.One simplified explanation of such a preference is that a tensilegrowing layer can compensate to some extent the strain of the naturallycompressed substrate surface, as well as the fact that the tensilegrowth provides conditions for thicker pseudomorphous growth that arealso more favorable for 2D (layer) growth, which is the reason forobserving smooth surface morphology after such growths. In contrast,when the growth occurs under compressive strain, such growth conditionsallow a smaller critical thickness and favor 3D (island) growth instead,which results in rougher surface morphology. That is why, for example,growth of CdS/InP (−0.624% lattice mismatch) should be preferred to thegrowth of InP/CdS (the same but positive, +0.624%, lattice mismatch).However, such considerations may depend on what we want to achieve withthe growth, whether metamorphic buffer layers or the formation ofquantum dots, wells, or other nano or microstructures.

It should also be remembered that the thermal mismatch between thegrowing layer and the substrate, i.e. the difference between the thermalexpansion coefficients and their thermal conductivities, starts to playa more and more important role with increasing the layer thickness,which can lead to cracking of the growing layer. For example, the 3times smaller thermal conductivity of ZnSe (18 W·m-1K-1) but largerthermal expansion coefficient (compare 7.1 vs. 5.7 10⁻⁶·K⁻¹) (see FIG.26 ) should be also taken into account when the intention is growingthicker ZnSe layers on GaAs substrates.

In general, the best ternary for the buffer layer will be the one thatis formed by the two parenting materials. For example, GaAsP sounds likethe best buffer layer material for the GaP/GaAs or GaAs/GaP growths. Forthe purpose, the initial growth shall be initiated under the flow of amixture of AsH₃ and PH₃. In this case, the ratio of these two precursorsin the mixture may be changed from only arsine (AsH₃) to only phosphine(PH₃) in order to build up a graded GaAsP ternary buffer layer. However,if we want to grow a thick GaAsP ternary layer (not only a ternarybuffer layer), we shall keep a desired precursors' ratio constant, toobtain a constant layer composition. One should also keep in mind thatphosphine is much more volatile than arsine, which means that to achieveequal amounts of phosphorus and arsenic in the ternary composition, theamount of phosphine in the AsH₃+PH₃ ratio shall be much greater thanarsine. In this example, the III-group element (Ga) is the same in thesubstrate and the layer material. Similar to this example is the growthof GaSe on GaAs. In this case, the ternary GaAsSe shall be formed byusing one boat of molten Ga over flowed by a mixture of arsine (AsH₃)and hydrogen selenide (H₂Se). Similar is also the case of growth of GaSbon GaAs, where a mixture of arsine and hydrogen antimonide (called alsostibine), AsH₃+ SbH₃, flows over the boat with molten Ga, to form theGaAsSb ternary. The cases of growths of layers on substrates when theIII-group element of the layer and substrate are different, however, aremore complicated. Thus, according to one study GaSb has been grown(using a different growth technique, MBE) not only on GaAs substratesbut also on InAs and AlSb buffer layers deposited in advance on the GaAssubstrate. In these two cases (InAs and AlSb buffer layers) theIII-group elements, when growing the initial buffer layers on the GaAssubstrates, are different—Ga and In in the InAs/GaAs case and,respectively, Ga and Al in the AlSb/GaAs case. Towards this purpose, anadditional boat with molten In or, respectively, with molten Al isintroduced into the reactor chamber. As for the V or VI group elementprecursors, only one V-group element precursor, AsH₃, is needed for thegrowth of the InAs buffer layer, while in the case of the AlSb/GaAsgrowth we will need not only a V-group element precursor, AsH₃, to flowover the boat with the molten Ga but also one VI-group elementprecursor, SbH₃, to flow over the boat with the molten Al. In addition,making it even more complicated, after the deposition of the bufferlayer we proceed with the growth of the desired GaSb layer on the grownInAs or, respectively, AlSb buffer layer. For this purpose, in order toinitiate the GaSb/AlSb growth, the VI-group element precursor, SbH₃,shall be kept flowing over both the Ga and the Al boats, while the AsH₃flow shall be turned off. Respectively, in the case of GaSb/InAs growth,the VI-group element precursor, SbH₃, shall be turned on to overflow theboat with molten Ga, while the AsH₃ flow shall be kept flowing over theboat with molten In. Thus, the growth of GaSb on GaAs with theassistance of an InAs buffer layer (GaSb/InAs/GaAs) will start with thegrowth of an intermediate GaInAs ternary layer at the InAs/GaAsinterface. This with the involvement of SbH₃ will convert graduallythrough a GaInAsSb quaternary phase within the InAs buffer layer to aGaInSb ternary layer near the growing GaSb/InAs interface which,eventually, by reducing the In content (with reducing the AsH₃ flow overthe molten In) gradually will convert in the desired GaSb binary layer.Similarly, the growth of GaSb on GaAs with the assistance of an AlSbbuffer layer (GaSb/AlSb/GaAs) will start with the growth of anintermediate AlGaAsSb quaternary buffer layer at the AlSb/GaAsinterface, which will convert into an AlGaSb ternary at the GaSb/AlSbinterface, which eventually will convert in the desire GaSb binarylayer.

Another example with similar complexity is the growth of ZnSe on a GaAssubstrate. The growth in this case occurs with the involvement of one IIand one III-group element precursors (Zn and Ga) and two V-group elementprecursors (AsH₃ and H₂Se). However, this process could be simplified bynot involving AsH₃, if (similarly to the growths of GaP/GaAs orGaAs/GaP) the non-native VI-group element precursor (H₂Se) “attacks”during the pretreatment stage the surface of the GaAs substrates, withthe expectation that this ternary transition layer will graduallyconvert into ZnSe during the following ZnSe growth.

Other good examples of heteroepitaxy are the growths of ZnTe/GaSb (FIG.100 , ZnS/GaP, and CdS/InP substrates (FIG. 10J), which in theirsimplest cases proceed through the formation at the growing interface ofternary layers, GaSbTe or InPS, respectively. More examples forheteroepitaxy through intermediate ternary or quaternary buffer layers(or just thick growths of ternaries or quaternaries layers) aresupported in FIGS. 10A-10L and FIG. 13 .

In summary, the examples provided in the previous paragraphs considertwo different approaches for facilitating heteroepitaxial growth. Thefirst one is by “in-situ” growing of a ternary or quaternary bufferlayer between the substrate and the growing layer. The second one is bygrowing the intended layer on an already deposited buffer layer (itcould be by a different growth technique) from a material that,hopefully, has a close lattice and/or thermal match with at least one ofthe substrate or the growing layer. In many cases, multiple bufferlayers from different materials may be used to secure the desired smoothgradual transition between two materials that, at first sight, lookcompletely incompatible. One good example of that is the growth of InSbon a GaAs substrate. The first step in this growth is to grow anintermediate layer of InP (lattice constant 5.8668 Å) on the GaAssubstrate (lattice constant 5.6533 Å). The second step is to grow asecond intermediate layer of GaSb (lattice constant 6.0959 Å) on thefirst InP buffer layer. The next step is to grow a third intermediatelayer of ZnTe (lattice constant 6.1010 Å) on the second GaSbintermediate layer, and then to finish with the growth of a thick growthof InSb (lattice constant 6.4794 Å) layer. This was our initial goal,which, however, was not possible by a direct InSb/GaAs growth, due tothe huge positive lattice mismatch (+10.74%) between these twomaterials. Of course, the success of such efforts will be greatlyimproved if the intermediate layers are grown in mixtures of the relatedprecursors (in the case of the first InP/GaAs transition, an AsH₃+PH₃mixture in the presence of Ga and In overflowed by HCl, etc.), whichwill support the growth of ternary or quaternary intermediate layerswith a gradually-changing composition, ensuring a smooth transitionbetween the two materials. Thus, materials that are otherwise completelyincompatible may be grown on each other, even with differences in thelattice constants of 10 A or more.

In some cases, the substrate pretreatment may be successful with anon-native precursor that has nothing to do with the subsequent growth.An example of that is the pretreatment of a Si substrate with H₂Se inorder to prepare the Si surface for the following thick HVPE growth ofGaP. In this case, PH₃ had to be the first choice of a non-nativeprecursor for pretreatment of the Si substrate with the idea PH₃ to pitthe Si surface, starting to form GaPSi islands, which to coalesceeventually in a GaPSi buffer layer. The effect of PH₃ on the Sisubstrate, however, was not as strong as expected, as compared to theunexpectedly strong effect of H₂Se (FIGS. 24A-24B). As the SEM images inFIG. 24A (top surface) and FIG. 24B (cross section) indicated, H₂Se hasa significant beneficial impact on the Si surface, etching it, i.e.making it rougher. Considering that, in contrast to the cases of usingfar-from-equilibrium growth techniques (MOCVD or MBE), a direct HVPEGaP/Si growth is impossible due to the low EPD (only 10² EP/cm²—compared with the much higher numbers for GaAs and GaP provided above),the newly formed etch pits after the H₂Se pretreatment, by providingmore sites at the surface for the approaching atoms to adhere to, willfacilitate the HVPE GaP/Si growth, even without forming any ternarybuffer layer. Pretreatment of the substrate surface with a non-nativeprecursor, which is not expected to form a ternary or quaternary bufferlayer is another variation of our approach, described in this invention.

In summary, the major criteria for choosing the substrate and thegrowing material pair are:

-   -   1. The sign and the magnitude of the lattice mismatch between        the substrate and the growing layer: This determines the type of        the elastic strain built in the growing layer and the mechanisms        of its relief, as well the thickness of the pseudomorphous        growth (h_(c)) and which type of growth—2D (layer growth) or 3D        (island growth) is favored.    -   2. The difference in the thermal expansion coefficients and the        thermal conductivities of the substrate and the growing        material: The importance of this factor increases with increase        of the growing layer thickness.    -   3. The crystallographic structure (symmetry) and the chemical        bonds of both the substrate and the growing material and how        compatible they are to each other.    -   4. The maturity of the substrate growth technology, wafer        processing, and template preparation techniques.    -   5. The price, quality, and availability of the particular        substrate or patterned template.    -   5. The maturity of the growing technique for the growth of the        related layers.    -   6. The availability, toxicity, and flammability of the chemicals        used and how corrosive they are. In other words, are they        environmentally friendly and how dangerous they are for humans?    -   7. The range and importance of the expected practical        applications and, in general, are there alternative approaches        for preparing these materials and, if there are any, how        competitive are they to the approaches presented here.

Precursor Gases and Ternary-Forming Gases

The first precursor gas is usually hydrogen chloride (HCl) diluted tothe desired extent by the carrier gas (usually H₂). The role of theprecursor gas is to pick-up a II or III group element (e.g. Ga, Al, Zn,Cd, Hg, etc.) from an open boat or from a bubbler, and with it to form ametal-chlorine compound, called II or III group element precursor orcalled just “precursor”, which is delivered to the mixing zone, makingit available to participate in the growing process.

The second precursor gas, called ternary-forming gas, is usually ahydride or halide in which there is a V or VI-group element (AsH₃, PH₃,H₂Se, SbH₃, H₂S, HF, NH₃, etc.) diluted to the desired extent by thecarrier gas (usually H₂). The ternary-forming gas, which is actually theprecursor of the V or VI-group element, is to be delivered to the mixingzone, making it available to participate in the growing process,reacting with the first precursor gas. We call this precursor“ternary-forming” because the chemical reactions between the precursorgas and the ternary-forming gas, which hopefully will occur on thesurface of the foreign substrate rather than in the gas stream,resulting in the formation of ternary islands which, eventuallycoalescence to form a continuous ternary intermediate buffer layer.

Alternative names: The precursor gas may be called “precursor” of “theII or III group element” or “first precursor”. The ternary-forming gasmay be called “precursor of the V or VI group element” or “secondprecursor”.

By demonstrating that heteroepitaxy is possible and successful at largerlattice mismatches without using a specially-patterned template in aone-step growth process (preceded by substrate pre-growth pretreatment),we have eliminated the need for growth on patterned substrates at largermismatches, or the preliminary deposition of a thin MOCVD or MBE layer,or even the HVPE deposition of a low-temperature lower quality bufferlayer. The disclosed parameters of heteroepitaxy, e.g. the thickness ofthe pseudomorphous growth and the periodicity of the misfitdislocations, for some particular cases have established clear criteriaby which additional cases of heteroepitaxy may be deemed favorable.

The invention described herein is an innovative approach for pre-growthin-situ treatment of a substrate and the subsequent optimized thick HVPEheteroepitaxial growth on the substrate as a continuation of thepretreatment. The inventive approach applies discovered processparameters that secure a smooth transition between two differentmaterials, and the process is flexible enough to adapt these parameterseven at relatively large lattice and thermal mismatches. The evidenceprovided herein regarding the successful heteroepitaxial growths ofmaterials which are disfavored according to the known prior art orconventional wisdom supports the application of the inventive processover a wide range of semiconductor pairs of materials (or pairs of asemiconductor material with another type of material—for exampleoptical, ferroelectric, etc.) having differing degrees of lattice orthermal mismatches.

As mentioned above, the invention consists broadly of two steps: (1)pre-growth treatment of the substrate in order to initiate thereplacement of V (or VI) group atoms of the substrate with V (or VI)group atoms of the layer intended to be grown, and (2) heteroepitaxialgrowth on the pretreated substrate. The proposed approach allows plentyof opportunity for applying different process parameters, usingdifferent pretreatment and growth temperatures and regimes of theirachieving, pressures, durations of substrate pretreatment and growth,flow rates, and flow regimes, etc. The invention allows one to freelyadjust the process parameters with the major goal to accommodate thesubstrate and the layer material or two or more subsequent layermaterials to each other.

Alternative Variations:

-   -   1. Growths of one material or different phases of one material        on different crystallographic orientations of another material,        as the substrate and the layer material could be with the same        or with different symmetry: In some cases one crystallographic        plane of one material could match closer, i.e. have smaller        lattice mismatch, with one or another material or different        phases of one and the same material.    -   Example: Hexagonal GaN can be successfully grown on (111) GaAs        substrates, while cubic GaN can be grown on (100) GaAs.    -   2. Two or more different phases of the same material can be        grown successfully on completely different materials and,        wise-versa, two different materials (e.g. GaN, AlN, GaP, GaAs,        etc.) can be grown on different phases of one and the same        material (a cubic phase zinc blende gallium selenide Ga₂Se₃ and        hexagonal gallium selenide ε-GaSe).    -   Example: Ga₂Se₃ can be grown on GaP and on GaAs substrates,        while GaSe may be grown on GaN substrates (see also FIG. 13 )        and wise-versa, GaN and AlN can be grown on Ga₂Se₃, while GaP        and GaAs can be grown on GaSe.    -   3. A layer from one material can be grown on a buffer layer        comprising a third material that has a lattice constant between        those of the substrate and the growing layer: In this case, the        substrate and the layer materials are not “parenting” to the        buffer layer materials.    -   Example: GaSb can be grown on GaAs by using not only GaSb, but        also InAs or AlSb buffer layers.    -   4. Multiple buffer layers from multiple distinct materials can        be used for a gentle and gradual transition between two        completely incompatible materials.    -   Examples: 1) Growth of a InSb/ZnTe/GaSb/InP/GaAs multilayered        structure—Grow, first, an intermediate InP layer (lattice        constant 5.8668 Å) on a GaAs substrate (lattice constant 5.6533        Å). Then continue with the growth of a GaSb layer, (lattice        constant 6.0959 Å) on the already deposited InP layer. After        that grow a third, ZnTe layer, (lattice constant 6.1010 Å) on        the GaSb layer, and then finish with a thick growth of InSb        (lattice constant 6.4794 Å) on the already grown ZnTe layer; 2)        Growth of a ZnSe/GaAs/GaP/Se multilayered structure—In this        case, after the deposition of GaP on a Si substrate, the as        grown GaP layer shall be pretreated in AsH₃. As a second step,        GaAs is grown on the pretreated GaP layer. As a third step the        as grown GaAs shall be pretreated in the flow of H₂Se after        which growth of ZnSe shall be performed the pretreated GaAs        layer.    -   5. Growth of multilayered structures not only for fitting one        material to another through heteroepitaxy but also in support of        developments related to various applications.    -   Examples: 1) Successful growth of optical on electronic        materials, for example, GaP on Si may have huge impact on        developments in Optoelectronics; 2) Subsequent growths of        multiple layers from materials with different bandgap on the        same substrate could accelerate developments in both multicolor        detectors and large and small surface highly efficient solar        cells.    -   6. Heteroepitaxial growth of low dimensional (LD) and two        dimensional (2D) semiconductor materials through van der Waals        heteroepitaxy where the lattice mismatch does not play that        important role in contrast to the case of the classic        heteroepitaxy.    -   Examples: 1) Growth of LD Ga₂Se₃ on GaAs substrates (or OP-GaAs        templates); 2) Growth of 2D elemental (e.g. graphene) or        compound semiconductor materials such as InSe and other        chalcogenides, phosphides, arsenides, iodides, and oxides.    -   7. The proposed approach is applicable not only for III-V        compounds (e.g. GaAs, InAs, AlAs, GaSb, InSb, AlSb, GaP, InP,        GaN, AlN, etc.) but also for II-VI (e.g. ZnSe, CdSe, CdTe, HgTe,        ZnTe, CdS, etc.) and even III-VI (GaSe, InSe, GaTe)        semiconductor compounds. At the same time, it is not a strict        rule to grow one group's materials, on substrates from the same        group (e.g. an III-V group material on a III-V group substrate,        etc.), because some mixed cases may be more favorable from point        of view of, for example, lattice and thermal mismatch.    -   Example: The already realized case of growth of ZnSe (II-VI        group) grown heteroepitaxially on the III-V group GaAs        substrate.    -   8. Growth of a semiconductor material on a semiconductor        substrate with different crystal symmetry.    -   (Note: A particular case from variation 1, purposely extracted        to emphasize on its importance) Example: 1) Growth of hexagonal        GaN on cubic GaAs substrates    -   9. Growth of semiconductor materials on oxide (including        perovskites) or non-oxide (including CaF₂ and BaF₂) optical or        non-optical materials including with different chemical        composition and symmetry.    -   Examples: 1) GaP and GaAs can be grown on CaF₂ (lattice        mismatches of −0.21% and +3.50%, respectively); 2) growths of        AlSb/BaF₂ and GaSb/BaF₂.    -   10. Growth of non-ferroelectric semiconductor materials on oxide        or non-oxide ferroelectric materials including on patterned        ferroelectric materials with different chemical composition and        symmetry.    -   Examples: 1) Growth of GaP on plain LiNbO₃ at the large lattice        mismatch of +5.87%, which can be facilitate with the preliminary        deposition of a thin MOCVD or MBE GaP layer on the substrate; 2)        Growth of OP-GaP on orientation-patterned periodically pulled        Lithium Niobate (PPLN).    -   11. Growth of semiconductor materials on optical materials,        which are neither oxide nor ferroelectric materials.    -   12. The combination of one close-to-equilibrium growth technique        (HVPE) with one far-from-equilibrium growth technique (MBE,        MOCVD), makes it possible to grow heterostructures which appear        impossible according to the prior art, including growths on        common substrates, such as Si or Ge: The preliminary deposition        of a thin MOCVD or MBE layer that facilitate the HVPE growth can        be accepted as a pre-growth pretreatment of the substrate prior        the HVPE growth    -   Examples: 1) Growth can start with thin MOCVD or MBE growth of        GaP on Si and continue with thick HVPE growth of GaP on the GaP        intermediate layer, which may be continued with thick HVPE        growth of GaAs on the HVPE GaP layer, and then continued further        with thick HYPE growth of ZnSe on the HYPE grown GaAs, etc.; 2)        Growth can start with thin MOCVD or MBE growth of GaAs on Ge and        continued with thick HVPE growth of GaAs on the GaAs        intermediate thin layer, which may be continued with thick HVPE        growth of GaP on the HVPE GaAs layer, and then continued further        with thick HVPE growth of Ga₂Se₃ on the HVPE grown GaP, etc.; 3)        The unfavorable effect of the large lattice mismatch during the        growth of GaP or OP-GaP on a LiNbO₃ substrate or on an        orientation-patterned periodically pulled Lithium Niobate (PPLN)        can be greatly facilitated by the preliminary deposition of a        thin MOCVD or MBE GaP or GaAs (or from other suitable material)        layer on the LiNbO₃ substrate or OP template.    -   13. Seeking for alternative chemical solutions such as using        alternative precursors or alternative way to for delivering them        or in-situ preparing of unavailable precursors.    -   Examples: 1) Due to the high vapor pressure of Zn, the boat with        molten Zn during the growth of ZnSe could be replaced by        prepared in advance or in-situ Zn-rich ZnCl₂-solution; 2)        Instead of using an open boat with the molten II or III group        element (e.g. Ga, Al, etc.), the supply of this chemical element        can be done by using a bubbler and even another II or III group        element precursor (e.g. TMG (tri-metal gallium), TMA (tri-metal        aluminum, etc.); 3) If a precursor is either unavailable or        unstable, or it is a subject of serious hazardous limitations        (e.g. H₂Te), it could be prepared in-situ within the reactor        volume as a part of the very growth process.    -   14. Pretreatment of the substrate surface with a non-native        precursor for which is not expected to form a ternary or        quaternary buffer layer if this can facilitate the following        growth.    -   Example: If a direct HVPE growth of GaP on Si is intended, the        low EPD of Si (10² EP/cm²—compared to the much higher numbers        for GaAs and GaP provided in [0004]) is a problem. In this case,        PH₃ shall be the first choice of a nonnative precursor for        pretreatment the Si substrate with the idea PH₃ to pit the Si        surface forming GaPSi islands which, eventually, to coalesce in        a GaPSi buffer layer. The effect of PH₃ on the Si substrate,        however, is not strong enough. Fortunately, H₂Se has a        significant impact on the Si surface, etching it, i.e. making it        rougher. The newly formed etch pits after the H₂Se pretreatment,        by providing more sites for the atom approaching the surface to        adhere there, facilitate the HVPE GaP/Si growth, even without        initially forming of any ternary islands and, eventually,        ternary buffer layer.    -   15. Replacing the in-situ pre-growth treatment of the substrate        with a non-native precursor (or a mixture of precursors) can be        replaced by in-situ thermal or/and chemical treatments of the        substrate or through wet or dry etching (e.g. ion beam etching)        before introducing the substrate in the reactor chamber for the        following growth.    -   Example: It is known that with a certain etching procedure        hydrofluoric acid (HF) can remove the oxides layers from the        surface of a Si substrate. Using optimized etching procedures HF        may etch deeper the Si surface as the newly formed itch pits can        facilitate the following HVPE growth. In addition, a number of        other chemicals and procedures can also have the desire impact        on many other common substrate materials.    -   16. Doping or co-doping of the substrate prior or during the        first stage of growth could also be used to fit two different        materials during the HVPE heteroepitaxy, bearing in mind that        dopants can change dramatically the lattice constant of a        material, making in this way the lattice mismatch between        growing layer and substrate more acceptable. This “in-situ”        procedure could be replaced by doping the substrate prior to        introduce it in the reactor chamber using techniques such as ion        implantation. Other techniques (e.g., ion beam spotter        deposition) may also facilitate the initials stage of the HVPE        growth.

While the present invention has been illustrated by a description of oneor more embodiments thereof and while these embodiments have beendescribed in considerable detail, they are not intended to restrict orin any way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. The invention in its broader aspects is thereforenot limited to the specific details, representative apparatus andmethod, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thescope of the general inventive concept.

What is claimed is:
 1. A method of performing heteroepitaxy, comprising:exposing a substrate to a carrier gas, a first precursor gas, a GroupII/III element, and additional precursor gasses (V/VI group precursor),to form a heteroepitaxial growth of one of GaSb directly on thesubstrate; wherein the substrate comprises ZnTe, and; wherein thecarrier gas is H₂, wherein the first precursor gas is HCl, the GroupII/III element comprises at least one of Ga; and wherein the additionalprecursor gasses comprise at least two or more of H₂Te (hydrogentelluride) and SbH₃ (hydrogen antimonide, or antimony tri-hydride, orstibine); flowing the carrier gas over the Group II/III element;exposing the substrate to the additional precursor gasses in apredetermined ratio of first additional precursor gas to secondadditional precursor gas (1tf:2tf ratio); and changing the 1tf:2tf ratioover time.
 2. The method of claim 1, further comprising: flowing theadditional precursor gasses through the furnace at a 1tf:2tf ratio ofabout 1:0; heating the substrate to about 500° C.-900° C.; and changingthe 1tf:2tf ratio toward 0:1 over a time period of 1 min-10 hours.